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Full text of "Dental and oral radiography : a text book for students and practitioners of dentistry"

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West Virginia University Libraries 

3 0802 102296254 7 




Dr. Claude H, Layman 


Digitized by the Internet Archive 

in 2012 with funding from 

LYRASIS Members and Sloan Foundation 














Copyright, 1916, by The C. V. Mosby Company 

Press of 

The C. V. Mosby Company 

St. Louis 


This book has been written primarily as a text book 
for students of dentistry. It is essentially a book for 
beginners, and as the majority of the dental profession 
are at present to be regarded as beginners in this com- 
paratively new branch of dentistry, the author enter- 
tains the hope that it will prove of interest to practic- 
ing dentists who appreciate the value of the x-ray, and 
are desirous of adding radiography to their accomplish- 

A few years ago the x-ray was considered in the light 
of a cultural asset to dentistry, but today the far-seeing 
members of our profession have awakened to the fact 
that it is a real necessity. 

The x-ray will give the maximum amount of service in 
dental practice only to such of our profession who mas- 
ter the technic of radiography, and in addition are pos- 
sessed of an accurate knowledge of the anatomy and 
pathology of the dental and oral structures. 

The author is indebted to the pioneers in dental radi- 
ography who have so generously contributed to its litera- 
ture. Of these, much of value has been derived from the 
writings of such men as A. H. Ketcham, Weston Price, 
Sidney Lange, Howard E. Raper, F. L. R. Satterlee and 
Edw. H. Skinner. 

During the preparation of this work, the author has 
been aided by various manufacturers of x-ray equipment 


who have generously furnished cuts whenever requested. 
Grateful acknowledgment is also made to Dr. J. R. Mc- 
Coy and to Laura Spruill who have made the drawings 
used as illustrations, and last and by no means least, to 
the publishers who have through their forbearance and 
mairy courtesies, lessened the burdens of the writer. 

James D. McCoy. 
Los Angeles, Calif. 



The Nature of the X-Ray and its Discovery .... 17 


High Tension Electric Currents — Magnetism — Electro- 
magnetic Induction 29 


X-Ray Machines. Rhumkorff or Induction Coil — Tesla 
or High Frequency Coil — Interrupterless Trans- 
former 43 

Requisites of the Dental X-Ray Laboratory .... 64 

Technic of Dental and Oral Radiography 79 


Technic of Dental and Oral Radiography (Continued) 109 

Development of Plates and Films 122 

The Interpretation of Dental and Oral Radiographs . 127 


Dangers of the X-Ray and Methods of Protection . . 145 



1. William Conrad Rontgen 20 

2. Michael Faraday 22 

3. Sir William Crookes 24 

4. Henrich Hertz 26 

5. The action of iron filings in forming definite curved lines 

about an ordinary bar magnet 34 

6. Diagrammatic illustration of the magnetic lines of force 35 

7. Diagrammatic illustration of the magnetic field surround- 

ing a coil of wire through which an electric current 

is passing 36 

8. An iron bar placed within the windings of a solenoid is 

subject to its magnetic field and becomes a magnet 37 

9. Magnet with diagrammatic illustration of magnetic lines 

of force surrounding it 39 

10. Battery from which an electric current is passing through 

the solenoid 40 

11. Diagrammatic illustration of the essential parts of an 

induction coil 44 

12. Diagram of the electrolytic interrupter 47 

13. Diagram of the induction coil 48 

14. Induction coil adapted for use in the dental x-ray lab- 

oratory 51 

15. Same as Fig. 14 52 

16. Same as Fig. 14 53 

17. Diagram of the high frequency coil 55 

18. Small type high frequency coil 56 

19. Medium-sized high frequency coil 56 

20. Large type high frequency coil 57 

21. Working principles of the interrupterless transformer . 59 

22. Interrupterless transformer adapted for use in the dental 

x-ray laboratory 60 

23. Same as Fig. 22 61 

24. Same as Fig. 22 62 

25. Diagram of an x-ray tube 65 



26. The coil or transformer tube 67 

27. The high frequency tube 68 

28. Connecting tube to x-ray machine 69 

29. The tube stand 71 

30. Illustration of how the tube may be placed at any de- 

sired angle 74 

31. Illustrating the reasons for using the tube shield, com- 

pression diaphragm, and compression cylinder . . 75 

32. Lead glass tube shield 76 

33. A convenient manner of arranging the necessary ap- 

paratus when not in use 77 

34. The patient holding the film in position against the 

upper teeth 85 

35. Correct and incorrect technic 87 

36. Technic for the upper molar teeth 89 

37. The patient holding the film in position against the 

lower teeth 90 

38. Procedure for making complete radiographic examina- 

tion of dental arches 92 

39. Arrangement of dental chair allowing patient's head to 

rest easily and firmly upon it 94 

40. The arrangement of the apparatus preparatory to seat- 

ing the patient 96 

41. The patient seated and the apparatus arranged for 

making a radiograph of the left side 97 

42. Technic for left side 99 

43. Technic for right side 100 

44. The result of correct technic 101 

45. Incorrect technic 102 

46. The result of incorrect technic 103 

47. Technic for radiographing areas in the upper and lower 

jaws extending from the median line to the first 

premolar 104 

4S. Technic for radiographing structures at the median line 

including the incisors, both above and below . . . 105 

49. Supporting the patient's head by a bandage of gauze 

to insure perfect immobility 106 

50. Connecting the tube to the x-ray machine Ill 

51. Diagram of an x-ray tube 115 

52. Radiograph showing an impacted upper third molar . 130 



53. Radiograph showing a cuspid tooth lying against the 

anterior -wall of the antrum 131 

54. Radiograph showing a supernumerary second bicuspid 132 

55. A radiograph to determine the state of dentition of the 

right side in the mouth of a child eleven years old 133 

56. A radiograph in which the successors to the deciduous 

teeth, as well as the developing second and third 
molars, are shown 131 

57. A radiograph in which a very large alveolar abscess is 

visible below the mesial root of a lower molar . . 135 

58. Radiograph showing an alveolar abscess involving the 

roots of an upper central incisor and lateral incisor 135 

59. Radiograph in which an abscess is visible between the 

central and lateral incisors 136 

60. Radiograph showing alveolar abscesses about the roots 

of the first and second bicuspids 136 

61. Radiograph showing alveolar abscesses above two bi- 

cuspid teeth 137 

62. Radiograph showing large alveolar abscess about the 

apex of the upper first bicuspid 137 

63. Radiograph showing large alveolar abscesses emanating 

from the upper lateral incisor and extending to the 
adjacent central incisor and cuspid 138 

64. Radiograph showing chronic alveolar abscess cystic in 

character above an upper lateral incisor .... 138 

65. Radiographs showing an upper bicuspid tooth with al- 

veolar abscess before and after treatment . . . 139 

66. Radiograph showing a necrotic area lying below a lower 

cuspid 140 

67. Radiograph showing an area of necrosis about the roots 

of a lower first molar 141 

6S. Radiograph showing differentiation of small wires in- 
troduced into the tooth and root canal fillings or 
tooth structures 142 

69. Radiograph showing root canal filling material forced 

beyond the root apex of an upper second bicuspid . 142 

70. Radiograph showing an abscess involving the perice- 

mental and alveolar tissues about an upper first 
bicuspid 143 

71. Radiograph showing an osteo-sarcoma of the mandible 143 





In order to gain an intelligent conception of 
the x-ray it is quite necessary that the student 
start with a consideration of certain phases of 
electro-physics, and radiant energy, or in fact 
the very foundation of matter itself. 

According to the most plausible theories and 
beliefs, all matter is suspended or contained in the 
medium known as ether, which is an elastic me- 
dium filling all space, interatomic and interelec- 
tronic, as well as all other space of which we have 
any knowledge. 

Furthermore, many facts brought out by the 
close study of chemistry and physics seem to jus- 
tify the belief that all substances of matter are 
composed of minute particles called molecules, 
and that each molecule is made up of two or more 
elements called atoms, while these atoms are also 
further divided in particles known as electrons. 

These electrons or units of matter are never 



still, but are in a constant state of motion or vi- 
bration, each substance having its own specific 
atom and the electrons of snch atoms having their 
own rate of vibration. 

The vibration of these electrons produce dis- 
turbances in the ether known as " ether waves" 
which vary in length according to the rate at 
which electrons are vibrating. If the rate of vi- 
bration of the electrons be changed or disturbed 
there is a change in the ether waves, resulting in 
a corresponding change in the phenomenon pro- 

If this theory of matter is correct, as the evi- 
dence of modern science would lead us to believe, 
all matter then is made up of the same constitu- 
ents, and its various forms are determined not 
by any essential difference of composition, but 
by the number, arrangement and amount of mo- 
tion of the ultimate particles making up the atom. 

All this has a practical significance to us in un- 
derstanding the phenomenon which we call the 
x-ray. As stated before, it is known that a cer- 
tain rate of vibration of electrons will produce 
other waves resulting in a definite phenomenon, 
while a change in this rate will produce an entirely 
different phenomenon. For instance, a slow rate 
of vibration (75,000,000 per second) produces 
what are known as electro-magnetic waves. A lit- 
tle higher up the scale where the electrons are 
made to vibrate faster, heat waves appear. An- 
other increase and light waves appear. If we 


continue to accelerate the rate of vibrations of 
the electrons, there will be produced successively 
ultra-violet or Finsen rays; then cathode or rad- 
ium rays, and finally the x-ray. 

It will then be seen that the x-rays are produced 
as the result of the most rapid rate of vibration 
of which we have any knowledge. In the labora- 
tory this phenomenon is produced by the sudden 
stopping of a stream of rapidly moving free elec- 
trons in a vacuum tube which has been exhausted 
to one millionth of an atmosphere. 

The x-ray therefore may be defined as that form 
of radiation which emanates from a highly ex- 
hausted tube when an electric current of high ten- 
sion is passed through the tube. The object of 
the vacuum tube is to establish a medium in which 
all source of resistance is removed, so that the 
electric current may excite the exquisitely rapid 
vibrations necessary to produce the phenomenon 
desired, the electric current being the source of 

The radiation thus produced gives neither heat 
nor light, nor can it be deflected, reflected, or po- 
larized. In fact, it can only be recognized by 
its effect upon the photographic plate and upon 
such chemicals as "Willemite, Calcium, and Tung- 
state, which floresce or glow under its influence. 

The Discovery of the X-Ray 

The x-ray was discovered in 1895 by William 
Conrad Rontgen, Professor of Physics, at the 


Royal University of Wiirzburg, in Germany. 
This discovery marking as it did a distinct epoch 
in the Science of Medicine, was received by the 

Fig. 1. 
William Conrad Rontgen. 

world with incredulity and amazement, for its 
reported possibilities savored almost of the occult. 
''A new ray had been discovered by means of 


which it was possible to look through opaque sub- 

While it fell to the lot of Prof. Eontgen to make 
this discovery, there is no doubt but what other 
experimenters in the field of physics, unconscious- 
ly produced this same ray. In fact, its discovery 
was made possible by the work of other scientists 
who preceded Eontgen and laid the foundation for 
its advent. 

Of these Michael Faraday was the pioneer. In 
1831 he discovered electric magnetic induction, 
which made possible the induction coil and the 
other electrical machines utilized to generate cur- 
rents of great potential. As early as 1838 he con- 
ducted a series of experiments to determine the 
effect of electrical discharges upon rarified gases, 
and invented the terms "anode" and "cathode" 
for positive and negative electrodes. 

In 1857 Geissler constructed the first vacuum 
tubes and it was noted at this time that an elec- 
trical discharge passed through these tubes would 
produce a peculiar glow or phosphorescence, the 
coloring of which depended upon the character 
of the rarified gas contained in the tube. This 
phenomenon became known as "florescence." 

A few years later (1860) Prof. HittofT, a cele- 
brated physicist of Minister, conceived the idea 
of exhausting the Geissler tube to a higher de- 
gree of vacuum and found as a result an increased 
resistance to the passing of the electrical dis- 
charge, and that the color of the rarified gases 



under florescence, varied with the degree of rari- 
fication. He also discovered another fact which 
was to have an important bearing upon the work 

Fig. 2. 
Michael Faraday. 

of later experimenters, and that was that the lum- 
inous discharge in a Geissler tube, could be de- 
flected by a magnet. 


The important work of these early experimen- 
ters was followed later (1878) by Sir William 
Crookes, who succeeded in constructing a more 
perfect vacuum tube, that is, one which could be 
exhausted to a much higher degree of vacuum. 
With these improved tubes, Crookes discovered 
that with a sufficiently high vacuum the luminous 
glow within the tube disappeared, and demon- 
strated that within it there was a rectilinear radi- 
ation from the cathode, which he conceived as be- 
ing a projection of particles of highly attentuated 
gas at exceedingly high velocity. To this radiation 
he gave the name ' ' Cathode Rays, ' ' and because 
of the peculiar behavior of gas in this exceedingly 
rarified state, he concluded that it was as differ- 
ent from gas in its properties as ordinary air or 
gas is different from a liquid. He found that the 
impact of the cathode rays against the wall of 
the tube would produce within it a greenish 
"phosphorescence" or "florescence" and an in- 
crease in temperature ; also that these rays could 
be intercepted by metallic plates within the tube. 
By concentrating the rays at the focus of a con- 
cave cathode, he was able to produce a brilliant 
florescence and a very high temperature, both at 
the walls of the tube and in various substances 
within it. Without doubt, Sir William Crookes 
unconsciously produced the x-ray in the course 
of these experiments. 

In 1892 Prof. Heinrich Hertz discovered that 
cathode rays would penetrate gold leaf and other 



thin sheets of metal placed within the tube. Soon 
after this discovery, Hertz died, and his experi- 
ments were continued by his assistant, Lenard, 
who was able to demonstrate that many of the 
phenomena of the cathode rays could be observed 

Fig. 3. 

Sir William Crookes. 

outside of the Crookes tube. By closing a vacuum 
tube at the end opposite the cathode with a thin 
sheet of aluminum, he demonstrated that a radia- 
tion proceeded through or from the aluminum 
walls of the tube which would pass through many 
substances opaque to ordinary light, and after 


passing through such substances, it would excite 
florescence in crystals of barium platino-cyanide, 
and would effect sensitive photographic plates in 
much the same manner as ordinary light. Lenard 
considered that all these phenomena were due 
to the cathode rays alone although in the light of 
our present knowledge, there is no doubt that 
not only in his experiments but in those of 
Crookes, Hertz, and other investigators, x-rays 
were produced. However, they were not recog- 
nized as such until 1895 when Prof. Rontgen star- 
tled the world by the announcement of his dis- 

Upon the memorable day of his discovery, Prof. 
Rontgen was duplicating one of Lenard 's experi- 
ments in the laboratory of the TViirzberg Univer- 
sity. The experiment consisted of passing an 
electric current through a Crookes tube covered 
with black cardboard, to test its florescence upon 
a piece of cardboard coated with barium platino- 
cyanide. A fresh specimen of this chemical had 
been prepared and spread upon the cardboard 
which was placed against the wall on the opposite 
side of the room to dry. The room was darkened 
and the current was passing through the tube, 
when to his amazement, Prof. Rontgen noticed 
that the chemically covered cardboard on the oth- 
er side of the room was glowing with a wierd flo- 
rescence. He approached the cardboard and in 
doing so passed between it and the Crookes tube, 
and beheld his shadow upon the cardboard. Pick- 



ing n p a book, he held it in front of the screen 
and noticed that it also cast a shadow. He then 
discovered that the luminous glow or florescence 
on the cardboard appeared and disappeared with 
the turning on and off of the current. With the 

Fig. 4. 
Ileinrich Hertz. 

tube operating, he picked np the cardboard and 
while examining it, noticed the shadow of his hand 
on its surface, the bones appearing much darker 
than the soft parts of the hand. He also found 
that the florescence was produced in the card- 
board regardless of whether the chemically coated 


side was turned toward or away from the Crookes 
tube, showing that the rays had the power to pene- 
trate substances at a distance from the tube. 

Further investigation proved that the radiation 
producing these phenomena emanated from the 
point of impact of the cathode rays against the 
glass wall of the Crookes tube, that nearly all sub- 
stances were transparent to it, although in widely 
different degrees, varying roughly with their den- 
sity; that the radiation was rectilinear, that it 
could not be refracted, reflected, or deflected by 
a magnet. Hence it was plain to Kontgen that 
these rays were quite different from the cathode 
rays of Crookes, Hertz or Lenard. 

Using photographic plates wrapped in black 
paper to protect them from ordinary light, he ob- 
tained with these new rays shadow pictures of 
metallic objects in a wooden box, and of the bones 
of the hand. 

He continued his experiments both with the flo- 
rescent screen and the photographic plate, and in 
December, 1895, communicated his discovery to 
the Physico-Medical Society of Wurzburg. Be- 
ing unable to determine the exact nature of this 
new ray other than classing the phenomenon as 
longitudinal vibrations of ether, Rontgen called 
it the x-ray, the letter x representing the un- 
known in the mathematical formula. Even today 
the exact nature of the rays has not been deter- 
mined, although the concensus of opinion seems 
to be that they are violent ether pulses set up by 


the sudden stoppage of the cathode rays as they 
strike upon the walls of the tube or upon any in- 
tervening obstruction. If this theory be correct, 
x-rays are of the same general nature as light 
waves, but of such short wave length that they 
lie outside the visible spectrum. 



High Tension Electric Currents 

As stated previously, the x-ray is produced 
when an electric current of high tension is passed 
through a vacuum tube. Therefore, let us con- 
sider the character of this current and the means 
employed to produce it. 

There are several kinds of electric currents, 
but of these we need concern ourselves only with 
two — the direct current, commonly designated by 
the abbreviation D.C. ; and the alternating cur- 
rent, designated as A.C. 

The direct current is one in w T hich the electric- 
ity flows along a conductor in one direction at a 
uniform rate of pressure, while the alternating 
current flows along a conductor first in one direc- 
tion, then reverses and flows in the opposite di- 
rection, these changes taking place with great 
rapidity (50 to 120 per second). Such a current in 
making these changes is said to have completed a 
cycle, and its frequency is designated by the num- 
ber of alternations which occur each second. 

A high tension current is one which has high 



voltage or as it is expressed in electrical terms, 
lias great electromotive force, or pressure. 

The Volt is defined as the unit of electromotive 
force, and is analogous to the pressure caused 
by a difference in level of two bodies of water 
connected by a pipe — the pressure tends to force 
the water through the pipe and the electromotive 
force or voltage tends to cause the electric current 
to flow along a conductor. 

The Ampere is the unit of current strength, or 
in other words, the amount of current passing 
a given point on a conductor in a given time. If 
we again use the analogy of the two bodies of 
water at different levels connected by a pipe, it 
would be the amount of water which could pass 
through the pipe in a given time. 

The Ohm is the unit of resistance. Just as the 
water in flowing through a pipe is resisted some- 
what in its passage by the friction offered by the 
surface of the pipe, or by the limited capacity of 
the pipe, so likewise the electric current is re- 
sisted in varying degrees in its passage along a 
conductor, the degree of resistance depending up- 
on the degree of conductivity of the material used 
as the conductor, its length, cross section, etc. 

The Watt is the unit of electromotive power or 
the ability of a current to do work. The wattage 
of a current is determined by the voltage, or pres- 
sure, and the amperage or quantity, the wattage 
of a given current being determined by multiply- 
ing the voltage by the amperage. 


From the foregoing then we see that the char- 
acter of an electric current is determined by sev- 
eral factors all of which must be taken into con- 

If we wish to know the strength of a given cur- 
rent, Ave have but to remember this strength will 
depend upon the pressure or electromotive force, 
and the resistance offered by the conductor 
through which the current is passing, just as the 
strength of a stream of water flowing from a tank 
would depend upon the pressure and the size of 
the pipe carrying the water. In other words, the 
strength of the electric current equals the pres- 
sure divided by the resistance. Reducing this to 
an equation we have — 

, volts _ _ E.M.F. 

Amperes equals -r — or C equals — =„- 

This is known as "Ohms Law" and is one of 
the fundamental laws upon which electrical sci- 
ence is based. This important law has two other 
forms which make it possible to learn the rela- 
tionship and amount of any of these three units, 
providing two are known. For instance, by trans- 
posing the formula of Ohms law, we have — 

Volts equals Amperes X Ohms, or E.M.F. 
equals CXR. 

If we wish to determine the resistance offered 
by a given conductor, we apply the formula as 
follows : 

Resistance equals Amperage 0r R " ec * uals ~~^CT^ 


As stated before, the current which is passed 
through the vacuum tube to generate the x-rays 
must be a current of high tension, or great pres- 
sure, or expressed in the terms of the units just 
described, it must have very high voltage. The 
ordinary lighting current of 110 volts is inade- 
quate, as this current is of far too low potential 
to pass through the tube, as the vacuum offers 
great resistance, a resistance which to the ordi- 
nary current amounts to an absolute nonconduc- 
tor. We are obliged, therefore, to make use of 
some means which will produce a current of great 
voltage, a current we will say of at least 75,000 
to 150,000 volts. 

To do this, we must make use of one of the 
electrical machines which can generate such a 
current by utilizing the principle of electromag- 
netic induction. Lest the student become con- 
fused, we will first review very briefly some of 
the elementary principles of electromagnetism 
and its relation to the production of the high ten- 
sion current necessary in x-ray production. 


Magnetism is the term applied to substances 
which have the property of attracting small pieces 
of iron. A material possessing this property was 
first found by the ancients at Magnesia, in Asia 
Minor, from which fact arose the name magnet. 

The natural magnet is an oxide of iron and is 
also called the lodestone. Artificial magnets can 


be made by rubbing a bar of hard steel with a 
lodestone, or with another artificial magnet, or by 
means of an electric current. Artificial magnets 
acquire the same magnetic properties which the 
lodestone or natural magnet possesses except that 
they acquire them to a much greater extent, and 
are therefore always used in preference to nat- 
ural magnets. 

In addition to the property of attracting small 
pieces of iron, magnets have other characteristics 
worthy of mention such as polarity, or the prop- 
erty of assuming, when suspended and perfectly 
free to move, a north and south position. The 
compass is quoted as a familiar example. 

At the ends of a magnet, or in other words at 
its poles, the greatest power of attraction exists. 
This is easily illustrated by placing one end of au 
ordinary magnet in some iron filings and with- 
drawing it. The filings will cling to it in great 
numbers, as they will likewise do to the other end 
of the same magnet if it too be placed in the 
filings. The middle of the magnet (or that por- 
tion midway between the two poles) however, 
does not possess this property, but as the ends 
are approached the attraction increases, until the 
poles are reached where the attraction reaches 
the maximum. 

In observing the action of the two poles of a 
magnet in attracting the iron filings, no particu- 
lar difference is observed. They both attract the 
iron filings. There is a difference, however, which 


may be shown by experimenting with two mag- 
nets, one of which should be suspended at its cen- 
ter like an ordinary compass, while the other is 
held in the hand. If the north pole of the mag- 
net held in the hand is moved near the north pole 
of the suspended magnet they will repel each 
other. Likewise if their south poles are ap- 
proached they will repel each other. But if the 

Fig. 5. 

The action of iron filings in forming definite curved lines about an 

ordinary bar magnet indicates that the magnetic field exerts its influence 

in certain definite directions which are called "the magnetic lines of 

north pole of one be placed near the south pole 
of the other they will attract each other. This 
shows that like poles repel each other, ivhile un- 
like poles attract each other. 

The space surrounding a magnet which is sub- 
ject to its influence is known as its magnetic field. 
The presence of this magnetic field is easily dem- 


onstrated by placing a magnet under a sheet of 
paper upon which iron filings have been evenly 
spread. By tapping the paper lightly, the filings 
will form into a series of curved lines extending 
from one pole of the magnet to the other pole, as 
illustrated in Fig. 5. The formation of these def- 
inite curves indicates that the magnetic field ex- 
erts its influence in certain definite directions 
which are called the lines of magnetic force. 

■ ^4 ' ' .- , 

i ; v \ 

/ / 

! » \ \ ^ S ' \ 

1 1 \ \ ^ ^ / 1 1 , 

Fig. 6. 
Diagrammatic illustration of the magnetic lines of force. 

These lines of force start at one pole of the mag- 
net, pass in curved lines around to the opposite 
pole, where they re-enter and pass on through the 
magnet again, so that if any line is followed 
through its entire length, one will eventually come 
back to the starting point, as shown in Fig. 6. 

It is by virtue of its magnetic field, that a mag- 
net has the power of attracting pieces of iron. 


When a piece of iron is brought under its influ- 
? a I : the 

time being lias its two poles. If the north pole of 
is brought se to a piece of iron, a 
south pole will be induced in the iron next to this 
north pole, and a north pole in the portion far- 
thest from it. The attraction is then exactly sim- 
ilar I fheattraeti nbetw :: two permanent mag- 

ts when two unlike p>:~ brought toget: 

Tliis action of a magnet in developing magnetism 
in iron placed in its magnetic field is called mag- 
"When a piece of iron is in contact with a mag- 
li the attraction 3 g test, but actual 

ssary to magnetize the iron as it m 
only be placed witliin the magnetic field, or in 


other words. witliin the magnetic lines of force 
of the magnet. 

Magnetism may be induced in iron in another 
way not yet described, and to us this is of great 
importance. If an ordinary electric current is 
through a coil of wire, the coil becomes 
equivalent to a magnet and rounded by a 

magnetic field similar to that of a bar magnet. 
S li a coil of wire is called a helix, and if its 


gth is many times its diameter, it is called a 
solenoid. Sin lenoid is surrounded by a 

magnetic field similar to tl magnet I s< 

Pig. 7 it follows that a solenoid is capable of 
magnetizing pieces soft iron and attrac: - 
them in the same way as does an ordinary steel 
mac. The magnetic field of a solenoid is 
ngesl within its windings and therefore if a 


bar of soft iron is placed within the coil, the bar 
will be much more strongly magnetized than if 
placed in any other position about the coil. Such 
a coil adapted to carry a current and provided 
with a soft iron bar or core is called an electro- 
magnet (Fig. 8). 

In order to permit the wire to be closely wound 
and at the same time to allow the current to pass 
through each turn, the wire must be covered with 
insulation throughout its length. It should also 
be remembered that the iron core within the 
solenoid remains a magnet only while the current 
is passing through the coil, as "only electric 
charges in motion produce magnetic effects." 

Electromagnets are much more powerful than 
ordinary magnets, that is, their fields have much 
greater strength, for the field of the electromag- 
net is equal to the sum of the field due to the 
core, plus the field due to the current passing 
through the coil. 

Thus far we have discussed the fact that a mag- 
netic substance in the field of an ordinary mag- 
net, or a conductor carrying an electric current, 
is magnetized. This phenomenon, we know, is 
due to magnetic induction. It is also a fact that 
an electric current may be induced in a conductor 
by causing the latter to move through a magnetic 
field. It makes no difference whether this field 
comes from an ordinary magnet or from an elec- 
tric charge passing through a conductor. This 
action of a magnet or of a current on a conductor 



moved in its field is called electromagnetic induc- 

Principles of Electromagnetic Induction 

If the ends of a coil of wire are connected with 
a galvanometer (Fig. 9) and the coil is moved 
down over an ordinary magnet, the galvanometer 

Fig. 9. 

A, magnet with diagrammatic illustration of "magnetic lines of force" sur- 
rounding it. B shows a coil of wire connected to a galvanometer, C. 

will show that a momentary electric current has 
passed through the coil. The current continues 
as long as the coil is in motion and ceases as 
soon as the coil is brought to rest. If the coil is 
withdrawn from the magnet, a current is also 
induced which flows in an opposite direction to 



the current which was induced when the coil was 
carried down over the magnet. 

These induced currents are produced by the 
field surrounding the magnet moving or cutting 
across the ivires composing the coil. If a cur- 
rent is passed through the coil it creates a mag- 
netic field, and on the other hand the movement 

Fig. 10. 

A, battery from which an electric current is passing through the sole- 
noid, B; C, large coil into which the smaller coil B is passed; D, galvano- 

of a magnetic held within the coil produces a cur- 

Asa solenoid is surrounded by a magnetic field 
similar to an ordinary bar magnet, it follows that 
if a solenoid carrying a current were thrust with- 
in (Fig. 10) another coil, induced currents will 
be produced in the latter. These induced cur- 


rents, as in the case where the magnet is used, 
only flow while there is a relative movement be- 
tween the magnetic field and the conductor. 
When the solenoid is passed into the other coil, 
the induced current will flow in an opposite direc- 
tion to the current floiving in the solenoid, and 
upon withdrawing the solenoid, the induced cur- 
rent will floiv in the same direction as the cur- 
rent in the solenoid. 

Suppose the two coils just described are placed 
one within the other (there being no current pass- 
ing) and while in this position a current is started 
in the inner coil. Upon the passage of the cur- 
rent in the inner coil, a momentary current is in- 
duced in the outer coil, just the same as if a mag- 
net had been moved within it, as shown in Fig. 
9. This induced current remains only while the 
current in the inner coil is increasing in value 
from zero to its normal strength. As soon as this 
normal strength is reached, the induced current 
ceases to flow. Noav if the circuit of the inner 
coil is broken and its current ceases to flow, at 
this instant another momentary current is induced 
in the outer coil, which flows in a direction op- 
posite to the current which was induced by start- 
ing the current. These two induced currents 
created by starting and stopping the primary cur- 
rent, or in other words, by "making" and " break- 
ing' ' the current, are not of equal strength, the 
one produced by the "break" of the current be- 
ing much the stronger. 


Such an instrument arranged with one coil 
within the other, but without any connection be- 
tween the two coils, is known as an "induction 
coil." The inner coil which is usually supplied 
with an iron core is known as the "primary coil" 
and the outer coil in which the current is induced 
is known as the "secondary coil." 

Induced currents are greatly intensified when 
soft iron cores are placed within the primary 
coils, as the cores become magnets and increase 
the strength of the field by adding largely to the 
lines of force therein. 

If an induction coil is constructed with the 
same number of turns of wire in the "secondary" 
as are present in the "primary," the current in- 
duced in the secondary will be exactly equal to 
the current passed through the primary. The 
voltage ivill not be increased. On the other hand, 
if the secondary contains twice as many turns as 
the primary, the induced current will be double 
the voltage of the primary, as each turn of the 
secondary induces a current in the turns directly 
adjacent to it, which must be added to the cur- 
rent induced in the first layer by the action 
of the primary current. Therefore, it should 
be apparent that as we increase the num- 
ber of turns in the secondary, we increase the 
E.M.F. or voltage. This increase of E.M.F. or 
voltage is due to the phenomena of " self-induc- 
tion " which is the principle utilized in all x-ray 
machines or other electrical apparatus used to 
"step up" the E.M.F. or voltage. 






The Rhumkorff or Induction Coil 

The Rhumkorff or "induction coil" which is 
the most common type of x-ray machine in use 
today, consists of two principal parts, each of 
which is a coil of wire, one being contained with- 
in the other, although they have no electrical con- 
nection (see Fig. 11). 

The inner coil or "primary" as it is called, 
consists of a few turns of very coarse insulated 
wire wrapped about a bundle of soft iron which 
is known as "the magnetic core." 

The outer coil or "secondary" is made up of a 
great many turns of fine insulated wire. It has 
been estimated that in a 12-inch induction coil 
the secondary coil is wound with between twenty 
and thirty miles of wire. This, of course, makes 
possible an enormous number of "turns of wire" 
so that when we consider that each turn of the 
secondary induces a current in the turn directly 
adjacent to it, which must be added to the current 




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is si? 



induced in the first layer by the action of the pri- 
mary current, the sum totum of the current com- 
ing from the secondary amounts to something tre- 

To compute the E.M.F. of the induced current 
(or that coming from the secondary) we have but 
to remember that "the E.M.F. of the induced 
current is to that of the primary current, as the 
number of turns in the secondary coil is to the 
number of turns in the primary." For instance, 
suppose Ave have an induction coil with 10 turns 
of wire in the primary, and 100 turns of wire in 
the secondary. If we pass a current of 110 volts 
through the "primary," the voltage of the "sec- 
ondary" current will be — 

i^X 100 = 1100 volts. 

Notwithstanding the great change in voltage 
the wattage of the secondary current is the same 
as it was in the primary, (except for a small loss 
due to internal resistance). This is not true, how- 
ever, of the amperage. For example, if the pri- 
mary current of 110 volts carries 5 amperes, its 
wattage would be 550. The wattage of the sec- 
ondary current would also -be 550, and since watt- 
age equals amperes multiplied by volts, the am- 
perage of the secondary current would be — 

550 17 A 
__^ = i/ 2 Ampere. 

Thus it will be seen that as the voltage or 


E.M.F. is increased in the before described man- 
ner, the amperage or current strength is de- 
creased in equal ratio. It should be plain, there- 
fore, that the original current running to the pri- 
mary is not changed in actual value, but is sim- 
ply transformed to a state or condition where it 
will do the special work required of it. 

In our consideration thus far we have consid- 
ered the manner in which an electric current may 
be transformed from a low to the high voltage 
necessary to energize an x-ray tube. We have 
not, however, named one important requisite of 
a current to be used for this purpose, namely that 
the current must flow continuously and in the 
same direction. 

In considering the manner of obtaining a cur- 
rent in the secondary, we learned that such a cur- 
rent is produced by "making" and "breaking" 
the primary current. If a continuous current is 
to be kept flowing, we must utilize some instru- 
ment which will rapidly "make" and "break" 
the current in the primary circuit. Such an in- 
strument is known as an "interrupter" and is 
essential to any induction coil. 

There are two classes of these instruments, 
both of which utilize some automatic principle, 
and are known as "mechanical" and "electroly- 

Mechanical interrupters, a simple illustration 
of which is the ordinary vibrator used on small 
coils, electric bells, etc., will rapidly make or break 



the primary current and thereby induce a fairly 
constant current in the secondary; but this form 
of interrupter has not been found to be as satis- 
factory for x-ray work as the electrolytic type. 

Of the various forms of electrolytic interrup- 
ters, the Wehnelt type is the one most universally 


P - 



Fig. 12. 

Diagram of the electrolytic interrupter. P, terminal of the positive 
electrode; N, terminal of the negative electrode; T, porcelain sheath or 
tube covering the positive electrode; I, platinum point of the positive elec- 
trode; L, negative electrode constructed of lead. 

used. It consists of a large battery jar which is 
nearly filled with, a solution composed of sul- 
phuric acid one part and water six parts. Into 
this solution are introduced two electrodes. The 





O tn 


C « 



c & 




P <u 


4> g 


negative electrode is constructed of lead and has 
a large surface exposed, while the positive elec- 
trode is contained within a porcelain or hard rub- 
ber tube extending down into the solution with 
only the tip or end of the electrode exposed. The 
tip of this electrode is usually made of platinum. 
(See Figs. 12 and 13.) 

The electrolytic interrupter is connected in the 
primary circuit and operates briefly as follows : 
As the current passes from the platinum point 
(the positive electrode) through the solution to 
the negative electrode, by virtue of its chemical 
action upon the solution bubbles of gas are formed 
around the exposed platinum point. These bub- 
bles act as a source of insulation and the current 
ceases to flow — "It is interrupted." At the in- 
stant it is interrupted, the bubbles are dispersed, 
the solution again comes in contact with the elec- 
trode, and the current is reestablished only to be 
broken again and so on, these changes taking 
place with tremendous frequency. With such an 
instrument the primary current may be inter- 
rupted from 60 to 30,000 times per minute. These 
interrupters are sometimes constructed with sev- 
eral platinum points which makes possible a 
greater amperage in the current without decreas- 
ing the rate of interruptions. For dental radiog- 
raphy, however, a single point interrupter will 
usually suffice, and at most, not more than a two 
point interrupter need be used. 

The interrupter, then, serves the purpose of 


creating the magnetic impulses which keep a con- 
stant current flowing from the secondary. "We 
should bear in mind, however, that the current 
produced by the "make" and "break" are not 
currents of equal strength, the current produced 
at the "break" having much the highest value. 
The fact that this current is the strongest, and 
that the magnetic impulses come from the same 
direction (as the induction coil is used on the di- 
rect current) it prevails over the weaker. There- 
fore the induced or secondary current which we 
use to energize the x-ray tube is the current which 
is created at the instant of the break. 

The other wave, or that created by the "make," 
is current in the wrong direction, and is called 
"inverse current." In some induction coils this 
inverse current is the source of much trouble and 
where it is present to any appreciable extent, will 
result in blurred radiographs. It can be con- 
trolled, however, by the use of "valve tubes," or 
a "spark gap," arranged in series with the x- 
ray tube, the valve tube or spark gap serving the 
function of cutting out the weaker or inverse cur- 
rent, without interfering to any appreciable ex- 
tent with the stronger current which is delivered 
to the terminals of the x-ray tube. 

The induction coil is used on the direct current 
of 110 or 220 volts. Where only the alternating 
current is available, some means must be used 
to change the current from alternating to direct 
before it enters the primary circuit of the coil. 



Fig. 14. 
Induction coil adapted for use in the dental x-ray laboratory. 

This change in the current can be accomplished 
by the use of "a rotary converter' ' of which sev- 
eral makes are available, or by a "chemical recti- 


Fig. 15. 

Induction coil adapted for use in the denial 
x-ray laboratory. 

Induction coiJ ada 

Fig. 16. 

Jabo d ra f t orv" Se in the dental x- 



tier." These rectifiers generally consist of two 
electrodes immersed in a solution of the phos- 
phate salts of potassium, sodium, or ammonium, 
one electrode being made of aluminum, and the 
other of lead, iron or carbon. When working 
properly, the current will flow to the aluminum 
through the solution, but not away from it, thus 
cutting out one wave of the alternating current, 
or it is possible, by properly connecting up three 
or four jars containing the electrodes, to utilize 
both waves of the current. 

Induction coils are usually rated as to power 
by the maximum width of the secondary spark 
gap. That is, the amount of distance the spark 
will jump between the secondary terminals. For 
example, a 12-inch induction coil is capable of 
producing a spark which will jump twelve inches 
of atmosphere. While these coils are made in 
various sizes, capable of producing a spark from 
six inches to forty inches in length, there is no 
particular advantage in using more than a 12- 
inch coil for dental radiography. (See Figs. 14, 
15 and 16.) 

Tesla or High Frequency Coil 

The Tesla or high frequency coil differs con- 
siderably in construction from the induction coil, 
although many of its principles are the same (Fig. 
17). In a way it is a double induction coil with 
the secondary of one coil acting as the primary 
of the other coil. An alternating current is util- 









a = 



ized in the primary of the first coil and by means 
of the secondary of this same coil is stepped up 
to a high voltage. This stepped up current is 

Fig. IS. 
Small type high frequency coil. 

Fig. 19. 
Medium-sized high frequency coil. 

then carried to a condenser. As the current 
leaves the condenser it is oscillating at a great 
rate of frequency and passes into the primary of 



Fig. 20. 
Large type high frequency coil. 


the Tesla or second coil where it induces a cur- 
rent in the s lary of this coil From the ter- 
minals of the last secondary, it is carried to the 
x-ray tube. The principles involved in this type 

apparatus are shown in Fig. 17. 

Like the current of the induction coil, the cur- 
rent from the Tesla coil is high in voltage and 
low in amperage, but unlike the current from the 
induction coil it is not uni-directional, but is al- 
ternating in character. Fur this reason, it is con- 
g ered by some as being less desirable for radi- 
ographic purposes. However this apparently ob- 
jectionable feature is overcome by using an x-ray 
tube constructed in such a way as to cut out one 
wave of the current and thereby produce practi- 
cally the same result as where an uni-directional 
current is used. 

These coils have the advantage of being less 
cumbersome, require less space and are less ex- 
pensive than the other form of apparatus, but they 
cannot be depended upon to do the character of 
work which the powerful "induction coil" or "in- 
terrupterless transformer" will do. Notwith- 
standing this fact, this type of apparatus undoubt- 
edly has a place in the x-ray laboratory of the den- 
tist, and if constructed along proper lines, can ren- 
der splendid service. Three sizes of these coiljs 
are shown in Figs. l x . 1!' and 20. 

Interrupterless Transformer 

The interrupterless transformer is the newest 

and by all means the mosl >owerful x-ray machine 



made. Aside from controlling and measuring ap- 
paratus, it consists of three principal parts, a ro- 
tary converter, if direct current is the source of 
supply, or a synchronous motor if the alternating 
current is the source of supply, a step-up trans- 
former, and a rectifying switch. 


Fie. 21. 

The working principles of the interrupterless transformer are here 
shown. The synchronous motor used to operate the rectifying switch of the 
alternating current machine may also be used as a rotary converter where 
the direct current is desired for other purposes in the laboratory. 



Two types of these machines are made, viz. : a 
direct current machine and an alteratins: current 

Fig. 22. 
Interrupterless transformer adapted for use in the dental x-ray laboratory. 

machine, the underlying- principles of which are 
shown in Fig. 21. 

When used on the direct current, the rotary 



Fig. 23. 
Interrupterless transformer adapted for use in the dental x-ray laboratory. 

Interrupted transformer adapted fof 

use in the dental x-ray laboratory. 


converter is set in motion and generates an al- 
ternating current which is sent through the pri- 
mary of the step-up transformer. This induces a 
current in the secondary of the proper voltage, 
but alternating in character. The rectifying 
switch then changes this current from an alter- 
nating to a direct current and as such it is de- 
livered to the terminals of the tube. 

The alternating current machine differs only 
from the direct current machine in that the alter- 
nating current is run directly into the primary 
of the step-up transformer. This induces a cur- 
rent in the secondary of proper voltage but al- 
ternating in character. The rectifying switch 
then changes this high voltage alternating cur- 
rent to a direct current, and as such it is carried 
to the terminals of the tube. 

The interrupterless transformer is, as stated 
before, the most powerful and efficient type of 
apparatus available for x-ray work. It is like- 
wise the most expensive, — too expensive in fact to 
be considered for the x-ray laboratory of the 
average practitioner of dentistry, in view of the 
fact that with the induction coil and other less ex- 
pensive apparatus such excellent results can be 

In Figs. 22, 23 and 24 several interrupter- 
less transformers adapted for use in the dental 
x-rav laboratory are shown. 



The requisites of a dental x-ray laboratory are 
not numerous but consist of — 

1st — A so-called x-ray machine. 

2nd — An x-ray tube. 

3rd — An adjustable "tube stand" for holding 
the tube, which should include a "tube shield' ' 
made of leaded glass, serving as a means of con- 
fining the rays and as a source of protection to 
the operator, and a lead "compression dia- 
phragm' ' and lead lined "compression cylinder.' ' 

4th — A photographic darkroom. 

As x-ray machines have already been discussed, 
let us now take up the others, in the order in 
which they have been given. 

X-Ray Tube 

The x-ray tube is a thin glass bulb six or eight 
inches in diameter, having two elongations or 
stems projecting from the bulb opposite and in 
line with each other (see Fig. 25). One of these 
elongations has within it a sheet iron tube at 
one end of which is a block of copper, faced with 
platinum or tungsten, and set at an angle of 45 
degrees. The other end of this sheet iron tube 



carries a platinum wire which is sealed into the 
glass at the end of the elongation and connected 
to a cap on the outside which serves as an elec- 
trical connection. 

The other elongation carries a rod at one end 
of which is a concave aluminum reflector, the 
other end being connected by means of a plati- 
num wire sealed in the glass to a cap on the out- 

A — Anode. 

U- -Assistant Anode 

C— Cathode 

D— Regulating 

F— Regulating Ad- 

G— Hemisphete 

H — Connection 

1— Assistant *node 

K — Anode Cap 

L — Cathode Cap 

M— Cathode Stream 

N — Focal Point 

Fig. 25. 
Diagram of an x-ray tube. 

side of the elongation, and also serves as an elec- 
trical connection. 

The concave reflector is known as "the cath- 
ode' ' and the metallic block opposite it and lo- 
cated upon the end of the sheet iron tube is known 
as the " target' ' or " anode." Above the anode 
and at an angle there is another stem projecting 
which carries a metallic terminal known as the 
"assistant anode." 




60 £ 


This assistant anode has a platinum wire ex- 
tending from it which is sealed into the glass and 
connected to a metallic cap on the outside of the 
tube. The outer terminals of the assistant anode 
and the anode are connected by means of a spiral 

Directly above the anode on the top of the tube 
there is a small chamber with an arm extending 
from it at right angles. This is known as "the 
regulating chamber/' The arm extension of this 
chamber is filled with asbestos impregnated with 
chemicals, and arranged about or within a metal 
from which a platinum wire extends, is sealed in- 
to the glass and connected to a metallic cap on 
the outside end of the chamber arm. 

Before being finally sealed, the tube is pumped 
to a high degree of vacuum (about 1/100,000 part 
of an atmosphere), only enough air being left in 
it to afford a path for the -passage of the electric 

Three general types of tubes are made for radi- 
ographic work, all of which embody the same gen- 
eral principles but vary according to the type of 
the machine upon which they are to be used. 

They are designated as follows: 

1. The coil tube. 

2. The transformer tube. 

3. The high frequency tube. 

Coil tubes and transformer tubes are similar 
in construction but not in vacuum (see Fig. 26). 
Coil tubes are exhausted to a much higher degree 


of vacuum in order to lessen the tendency for in- 
verse current, and give a high degree of penetra- 
tion. The transformer tube is made compara- 
tively low in vacuum as the current from the 
transformer is entirely free from inverse, and 
of such high voltage that the high vacuum is 
neither necessary nor advisable. 

P & 

Fig. 28. 

The high frequency tube differs slightly in con- 
struction from the coil and transformer tubes ow- 
ing to the fact that the high frequency current is 
not uni-directional. Therefore, a means must be 
resorted to for cutting away or disposing of one 
wave of the alternating current. This is accom- 
plished as shown in Fig. 27 by placing the anode 


or target in the position occupied in the coil tube 
by the assistant anode except that it extends 
down to the center of the tube. Then by having 
what really amounts to two cathode terminals, 
only one of which is focused against the face of 
the anode, and the other into a funnel in the back 
of the target, almost the same effect is produced 
as results from an uni-directional current. 

Connecting' the Tube to the X-Ray Machine 

In connecting up the tube to a coil or trans- 
former (Fig. 28), the anode terminal (A) is con- 
nected by means of a wire cord coming from a 
reel attached to the positive terminal of the ma- 
chine (A'), and the cathode terminal (C) is con- 
nected in a similar manner to the negative ter- 
minal of the machine (C). 

A third wire cord is usually run from a reel 
(R') situated on the coil near the negative ter-* 
minal to the cap on the regulating chamber (R). 
This third terminal on the coil has a spark gap 
between it and the negative terminal the length 
of which is adjustable (designated by S' and S). 

Operating the X-Ray Tube 

When the current is started in the machine it 
enters the tube at the anode and passes across 
the gap to the cathode, from which it is reflected 
back as the invisible cathode stream to strike a 
focal point on the target where the x-rays are 
formed and pass out through the walls of the 
tube (see Fig. 25). 

Fig. 29. 
The tube stand. 


With the passing of the current through the 
tube, it should light up in a characteristic man- 
ner, forming two hemispheres which have a def- 
inite line of demarcation. The hemisphere in 
front of the target which is the active hemisphere, 
is evidenced by a green florescence, the shade of 
coloring depending upon the degree of vacuum of 
the tube. The florescence of a highly exhausted 
tube will be a light yellowish green, a tube low 
in vacuum will show a bluish green, while a me- 
dium tube will be an intermediate green. 

For dental radiography, a fairly high tube is 
indicated and its vacuum should be kept as near- 
ly uniform as possible. This is made possible by 
utilizing the third terminal from the x-ray ma- 
chine. By placing the spark gap of this terminal 
about three or four inches from the negative ter- 
minal of the machine, the current will, when the 
vacuum of the tube gets high enough to resist its 
passage, pass over the gap, down the third ter- 
minal wire into the regulating chamber where by 
heating the asbestos it will liberate gas and there- 
by reduce the vacuum of the tube. 

Tube Stand 

The tube stand which serves the purpose of 
holding the tube, should be sufficiently heavy to 
support it against motion and vibration, and 
should be sufficiently adjustable so that the tube 
can be raised or lowered, or placed at any desired 
angle. Its base should be mounted upon castors 


so that it may be moved with ease. Sueli a tube 
stand is shown in Figs. 29 and 30. 

Tube Shield, Compression Diaphragm, and 
Compression Cylinder 

The tube, tube stand, tube shield, compression 
diaphragm and compression cylinder when ad- 
justed for work, as shown in Figs. 29 and 30, really 
comprise a single piece of apparatus. Bearing in 
mind the fact that the x-rays pass out in every 
direction from the face of the anode or target, 
(see Fig. 31- A) which is situated in the center of 
the tube, it is necessary, if the clearest possible 
shadows are to be produced, to use only those 
rays which have the same general direction and 
which have an equal amount of penetration. Now 
it is known that the most rapid and effective rays 
are those which pass out at right angles from the 
cathode stream designated by PR. Inasmuch as 
we desire to use these rays, and these rays only, 
in casting our shadows, we must establish some 
means of preventing the other rays (S,S,S,S) 
from escaping from the immediate area surround- 
ing the tube, and this is accomplished by means 
of the tube shield, compression diaphragm and 
compression cylinder. 

The tube shield (Fig. 32) a sectional diagram 
of which is shown in Fig. 31-B by T. S. is made 
of leaded glass, there being a sufficient amount of 
lead in the glass to prevent ordinary rays from 
passing through it. The compression diaphragm 

Fig. 30. 
Illustrating how the tube may be placed at any desired angle. 


Fig. 31-A. 

Fig. 31-C. 



makes up the floor of the tube shield (D), and is 
constructed of sheet lead with an opening of the 
proper size to allow the desired rays to pass 
through. The compression cylinder (CC) (Fig. 
31-C) is made of aluminum with a lead lining 
which absorbs any secondary rays which have 
succeeded in passing through the diaphragm. It 
should be apparent to any one that with this ap- 

ri g . 32. 

Lead glass tube shield. 

paratus, the only x-rays which succeed in leaving 
the immediate area of the tube are those which 
are used to cast the shadows of the parts desired, 
which is of great importance not only in obtain- 
ing radiographs which are sharp and clear and 
uniform, but also to the health of the operator 
and others associated with him in the office. 


i I 

Arrangement of the Apparatus in the Office 

If dental x-ray equipment is desired, the ques- 
tion naturally arises, where can the necessary ap- 
paratus be placed! While a separate room is de- 
sirable, it is by no means necessary as the ordi- 

Fig. 33. 
A convenient manner of arranging the necessary apparatus when not in use. 

nary operating room of "healthy size" can be 
made to accommodate it. 

The coil or transformer, and the tube stand 
can be placed against the wall at the left of the 
room, while the tubes can be hung in a suitable 
rack upon the wall where they will be out of 
harm's way (Fig. 33). Arranged in this manner, 


x-ray apparatus is not in the way, and is access- 
ible for nse at any time. 

The dental chair with its multitude of adjust- 
ments serves an important purpose in the dental 
x-ray laboratory, for the patient must be sup- 
ported in such a manner as to be able to hold per- 
fectly quiet during the time the exposures are 
made. Owing to the stability of the chair and its 
many adjustments, it will not only serve this pur- 
pose, but is preferable to having the patient lie 
upon a table which has been the method employed 
by many radiographers in the past. 

Photographic Darkroom 

Thus far we have discussed all but one of the 
requisites of the dental x-ray laboratory, viz. : the 
photographic darkroom. This is a very impor- 
tant requisite, and any one attempting to do radi- 
ography without it is greatly handicapped. It 
need not be large or elaborate, and running wa- 
ter is not absolutely essential, although it is an 
advantage. A closet 3%x5 ft. Avill suffice if noth- 
ing better is available. A broad shelf should be 
placed at one end to hold the developing trays 
and other photographic accessories. 

With a darkroom always available, the dental 
radiographer is able to develop his plates or films 
immediately, profit by their findings, or in case 
they do not come out satisfactorily, make others 
without subjecting the patient to the inconveni- 
ence of another appointment. 



Having discussed the requisites of the dental 
x-ray laboratory, let us now proceed to a consid- 
eration of their application in the actual work of 

The very nature of the structures with which 
we concern ourselves, their gross as well as mi- 
nute anatomy, renders them somewhat difficult to 
radiograph, and necessitates a refinement of tech- 
nic greater than that demanded with most of the 
other portions of the human anatomy. It would 
therefore seem obvious that an accurate knowl- 
edge and anatomic appreciation of the structures 
of the oral cavity and associated organs and 
structures is the first requisite for successful den- 
tal and oral radiography. 

We should keep in mind the fact that radio- 
graphs are shadow pictures, and that the effect 
produced by the x-ray upon the photographic 
plate is but a shadowgraphic representation of 
the tissues through which the rays have passed. 
We know that this ray penetrates all matter in 
inverse ratio to its mass or density, and therefore 
the shadow picture which is left upon the photo- 
graphic plate is simply a record of the varying 



density of the tissues through which the rays have 4 

The x-rays are particularly applicable to the 
dental and oral structures, owing to the fact that 
these structures differ enough individually in de- 
gree of density to permit of their appearing in a 
characteristic manner upon the photographic 
plate. For instance, it will be noted upon the ex- 
amination of a dental radiograph, that metallic 
fillings appear as white masses, and root fillings 
as somewhat less dense lines. The enamel and 
dentin are next in density, and root canals show 
plainly as dark channels in the dentin, wiiile the 
alveolar process and maxillae show their fine uni- 
form cancellous structure in various degrees of 
density depending upon their thickness. 

As a tooth is much more dense than the bony 
structures of the jaw, any anomaly of form, size 
or position in the jaws is easily discernible even 
though it occupy a position far from what might 
be expected; as for instance, impacted molars, 
teeth in the antrum, etc. 

The fact that the structures within the field of 
our specialty have a characteristic appearance 
under normal conditions, any alterations or 
change in these structures is at once evident up- 
on the plate. We thus are afforded a means of 
studying "intravitam" the gross pathology of the 
structures of the oral cavity. 

I would again emphasize a point previously 
made, viz. : that a radiograph is not a photograph, 


but a shadow picture which is produced by using 
the x-ray as the source of illumination and the 
photographic plate as a screen for recording per- 
manently the shadows cast. 

Therefore, in making radiographs, we must ad- 
here to the same rules which apply in making 
correct shadows with ordinary light. If correct 
shadows are cast, a certain definite relationship 
must exist between the source of illumination, the 
object and the screen. Any change or variance 
in this relationship will result in a changed im- 
age. A simple experiment will suffice to illustrate 
to a beginner the truth of this statement. 

Use a piece of ordinary white writing paper 
as a screen and hold it about two feet away from 
a lamp, and place your hand or any other small 
object, midway between the lamp and the impro- 
vised screen, and observe the shadow cast. You 
will note first, that it is very much enlarged ; and 
second, that it is very faint and indistinct. Now, 
slowly move the object toward the screen. As 
it approaches, the shadow becomes more distinct 
and smaller until at length when the object is 
almost touching the screen, the shadow will be 
good, black and distinct, and of practically the 
exact size of the actual object. It will also be 
found that the shadow can be altered by chang- 
ing the position of the light, that is, moving it to- 
ward the object or away from it, by lowering it 
below the level of the object or raising it higher 
than the object; or by moving it to the right or 


to the left. Eventually, however, a point can be 
found which will cause the shadow to assume its 
most correct proportions as well as its sharpest 
outline. When this point is established, the light 
rays will be traveling in a perpendicular direction 
to a plane which lies midway between the plane 
of the object and the plane of the screen, and the 
light will be placed at what we call the proper 
focal distance. 

Applying the laws deduced from this simple il- 
lustration of shadow making to radiography, we 
learn first, that the closer we can approach the 
photographic plate to the tissues we wish to show, 
the clearer and sharper will be the resulting radi- 
ograph; second, that the x-rays in passing 
through the tissues must travel perpendicularly 
to a line which lies midway between the plane of 
the tissues desired and the plane occupied by the 
photographic plate ; and third, that the source of 
the x-ray production (the target of the tube) 
must be placed at a proper focal distance. 

In order to obtain a radiograph of any portion 
of the body, it is necessary to have a photographic 
or x-ray plate, or film (properly prepared so as 
to exclude all light and moisture), placed in such 
a position that the rays passing through the 
structures desired, will register their shadows 
with the least amount of distortion possible upon 
the plate. 

In securing shadowgraphic representations of 
the dental and oral structures, two general meth- 


ods of procedure are open to us, each of which 
has its values and special indications. These are 
known as the "intra-oral" and "extra-oral" 

With the first, onl}^ small films are used which 
are placed within the mouth opposite the area to 
be radiographed, and held in position either by 
means of a tray or film holder, or by the assist- 
ant, or better still, by the patient exerting slight 
pressure with the finger. This method is indi- 
cated where radiographs of small areas only are 
desired, as, for instance, two or three of the teeth, 
with the adjacent alveolar process. 

With the other method of procedure mentioned, 
viz. : the "extra-oral" method, large plates or 
films are used and the areas desired are brought 
in as close contact as possible with the plate by 
pressing or resting the face against it. The x- 
rays are then passed through the structures from 
the other side of the skull, and oftentimes must 
pass through the entire face or skull, in transit. 

"When using this method, large areas may be 
radiographed, which in some instances will em- 
brace the lateral halves of both the upper and 
lower jaws from the cuspid region anteriorly to 
the angle of the jaw posteriorly, and from the 
floor of the orbit above to the inferior margin of 
the mandible below. In fact, it is possible by 
making several exposures to obtain in detail a 
shadowgraphic representation of the dental ap- 
paratus "in toto" as well as its associated or- 


gans and structures, the nasal cavity and pneu- 
matic sinuses, the maxilla and the mandible. 

It should be apparent to any one that the first 
method greatly reduces the possibilities of the 
x-ray. Both methods have their advantages and 
neither should be discarded in favor of the other. 

Intra-oral Method 

"We shall first discuss the intra-oral method by 
which small areas are radiographed. First of all, 
the patient should be placed in a comfortable 
position, and the head supported so that it may 
be held perfectly still. After the tube has been 
tested out and the proper degree of vacuum es- 
tablished, the tube stand (complete with the other 
apparatus before described) is moved to a posi- 
tion where the rays coming from the tube, through 
the compression diaphragm and cylinder can be 
made to pass through the desired areas and cast 
their shadows upon the small film within the 
mouth (Fig. 34). 

In using this method upon the upper teeth, the 
greatest care must be exercised if the shadows 
produced are free from distortion, for the film 
must be held within the upper arch against the 
lingual side of the teeth and the palate, and must 
occupy a position which is in a different plane 
from that occupied by the roots of the teeth. 
Whenever it is necessary to direct the rays upon 
structures which lie at an angle with the plate 
or film, correct shadows may be obtained by ad 


hering to the following rule: "Bisect the angle 
made by the plane of the object, and the plane of 
the film, and direct the rays so that they will 
fall perpendicular to this bisected plane." 

Failure to adhere strictly to this rule is one of 
the most common causes of partial or complete 
failure in producing true shadowgraphic repre- 

Fig. 34. 

The patient can hold the film in position against the upper teeth by- 
exerting slight pressure with the thumb. 

sentatioiis of the dental structures. For instance, 
if the rays are directed from too low a source, 
the shadows will be lengthened, or if they be di- 
rected from too high a source, the shadows will 
be fore-shortened, the amount of elongation or 


fore-shortening being in direct proportion to the 
amount of deviation from the proper focal point. 

The importance of adhering strictly to this rule 
is graphically shown in Fig. 35, * where an upper 
central incisor and the adjacent teeth are radio- 
graphed. In the upper picture (A) the rays are 
passing in from too low a source with the result 
that the image imposed upon the film is length- 
ened to the extent that the resulting radiograpli 
is useless. In the center picture (B) the rays are 
coming from too high a source, the result being 
a shortened image. Such a radiograph has but 
little value and in many instances would prove 
very misleading. In the lower picture (C) the 
rays are passing in at the correct angle, viz. : 
they are directed perpendicularly to a plane which 
lies midway between the plane of the teeth de- 
sired and the plane of the film. The result is a 
radiograph in which the images of the teeth de- 
sired are imposed upon the film in their correct 

It will be noted upon a close examination of 
this last radiograph (C) that an abscess is pres- 
ent upon the root of the right central incisor. By 
examining the other radiographs (A and B) it 
will be seen that this condition is not apparent in 
them, which lends emphasis to the importance of 
an exact technic. 

The technic illustrated (by C of Fig. 35) is in- 

*Technic of Dr. Weston Price. 


dicated for all of the upper teeth. Occasions may 
arise, however, where it will not suffice entirely 

Fig. 35. 
Correct and incorrect technic. 


for the upper molar teeth owing to the fact that 
the buccal roots and the lingual roots may diverge 
to the extent of assuming different planes. In this 
event, it may be necessary to make more than one 
radiograph, if information of an exacting char- 
acter is desired concerning an upper molar. The 
plan of procedure is shown in Fig. 36, A. B. and ( '. 

If a general picture of the molar is desired 
(shown by A) the plane of the tooth is assumed 
as lying midway between buccal roots and lin- 
gual root, and the rays are passed in perpendicu- 
larly to the plane lying midway between this as- 
sumed plane and the film. In the resulting radio- 
graph none of the roots will appear in their exact 
proportions, but the buccal roots will be slightly 
shortened, while the lingual root will be slightly 

When it is desirable to obtain a radiograph of 
the buccal roots in their exact length, they must 
be assumed as being the plane of the tooth (B) 
and the rays must pass in perpendicularly to a 
plane lying midway between them and the film. 
In this event, the image of the lingual root is 

If the lingual roots are under scrutiny (C) 
they must be considered the plane of the teeth, 
and the rays passed in perpendicularly to a plane 
lying midway between the lingual root and the 
film. In this event, the image of the Ungual root 
will have its correct pro portions, but the image 
of the buccal roots will be slightly shortened. 


Fig. 36. 
Technic for the upper molar teeth. 



The upper molars are by all means the most 
difficult teeth to radiograph. That is. to obtain 
radiographs which are as comprehensive as those 
made of the other teeth. However, by going to 
the extra work entailed by the foregoing proced- 
ure, valuable radiographic information can of- 
tentimes he srained. 

Fig. 57. 

The patient can hold the film in position against the lower tee- 
exerting slight pressure with the finger. 

With the lower teeth | Pig. 37 ) we do not have 

this difficulty to contend with to so great a de- 
_ ee, as the films can he placed for the most part 
in such a position that they lie parallel to the Ions: 
axis of the teeth, and the rays ran be directed in 
a perpendicular direction both to the plane of the 
teeth and the plane of the film. 


Lu placing the films in the mouth preparatory 
to making radiographs of the lower teeth, diffi- 
culty is sometimes encountered, owing to the fact 
that the tissues are usually quite sensitive. In- 
asmuch as the lilm must be \ ssed well down be- 
tween the tongue and the teeth, it is advisable to 
first see that no sharp corners exist on the film 
covering, or better still, provide a rubber envel- 
ope or film holder which has no sharp cur,. 
Such an envelope is easily improvised by the use 
of ordinary black vulcanite robber. A piece of 
this rubber which should he a little more than 
double the size of the film, is wrapped about it 
and the free edges pressed together. These ed_ - 
are then trimmed with a pair of scissors so that 
the corners are rounded. Such an envelope con- 
taining the film can be introduced into the mouth 
and placed well down on the lingual side of the 
t^eth with a minimum amount of discomfort to 
the patient. 

Where it is necessary to make a complete radi- 
ographic examination of the dental arches, it can 
be accomplished in the average case, by making 
six exposures of each arch. The procedure to be 
followed is diagrammatically shown in Fig. • v . 
The numbers l. ; ; . 3, 4. 5, 6 indicate the position 
of the x-ray tube in its relation to the dental arch, 
and the ends of the lines coming from the num- 
bers show the position of the mesial and distal 
edges of the film used for each exposure. It will 
noted that each adjacent film position over- 



laps its neighbor which is advisable so that no 
area is left out. 

In making radiographs of the anterior part of 
the arch, it is a mistake to attempt to radiograph 
more than two or three teeth at a time, as the 
curvature of the arch usually renders it impos- 
sible to get more than that number free from dis- 

Fig. 38. 

Another point in technic which should not be 
overlooked if sharp outlines are to be obtained, 
is the one in regard to having the tube placed at 
the proper distance from the structures to be 
radiographed. To establish the best focal dis- 
tance for work about the teeth or jaws, the tar- 
get of the tube should be about twenty inches 
from the plate or film. 

With a good x-ray machine, and a properly reg- 
ulated tube, good radiographs can be obtained by 


very short exposures, particularly by using the 
uitra-oral method, as the rays need only penetrate 
a comparatively short distance before reaching 
the plate. With the apparatus now available 
good radiographs can often be obtained by in- 
stantaneous exposures. However, instantaneous 
exposures are not necessary for good dental radi- 
ography. X-ray apparatus which is capable of 
producing sharp, clear "uitra-oral" radiographs 
in from two to five seconds, is efficient enough for 
use in the x-ray laboratory of the dentist. 

Extra-Oral Method 

The extra-oral method is in the author's opin- 
ion, the one offering the widest range of useful- 
ness in our work. As stated previously, this is 
the method used to obtain radiographs of large 
areas. Not only can larger areas be obtained by 
this method, but locations and structures inac- 
cessible to the small films are reached and their 
images accurately and clearly recorded upon the 
larger plates. Therefore, the advantage of this 
method is well founded. 

The technic is simple when once mastered, but 
must be adhered to accurately if the results are 
to be depended upon for diagnosis. In using the 
extra-oral method, large plates or films are used 
and the areas desired are brought in as close a 
contact as possible with the plate, by pressing or 
resting the side or portion of the face upon ivhich 


the structures desired are located, against the 

First of all, the patient must be placed in a 
position so that the head can be held perfectly 
still. The dental chair with a few adjustments 
offers an excellent means for accomplishing this. 

Fig. 39. 

The head rest of the dental chair with its many adjustments can easily be 
arranged so that the patient's head may rest easily and firmly upon it. 

One of the chair arms is lowered down against 
the side of the chair or removed, and the patient 
placed sideways in the chair. The chair back is 
adjusted so that the patient lies against it in an 
easy position, and the headrest wings are ad- 
justed so as to lie flat and thereby form an excel- 


lent resting place for the plate. The head rest 
with its many possible adjustments can easily be 
placed so that the patient's head rests easily and 
firmly upon the plate, rendering it an easy mat- 
ter to remain perfectly quiet. This position is 
shown in Fig. 39. 

Author's Method of Seating the Patient 

In the author's opinion, there is another meth- 
od of seating the patient for this character of 
work which necessitates less confusion in the of- 
fice than the method just described. It is accom- 
plished by using an ordinary chair with a straight 
back and small arms, placed against the back of 
the dental chair. The head rest of the Chair is 
turned over and adjusted to the proper height, 
position and angle, so that the patient's head can 
rest against it in any desired position. In this 
way the patient is afforded the firm support of 
the heavy dental chair, and therefore has little 
difficulty in remaining perfectly quiet, and the 
operator can by making a few changes in the posi- 
tion of the small chair, by moving and readjust- 
ing the tube stand and the head rest, have radio- 
graphic access to any part of the oral cavity or 
associated structures. The arrangement of the 
apparatus preparatory to seating the patient is 
shown in Fig. 40. 

The fact that this requires but a few moments, 
does not disarrange the office, or put the patient 
to discomfort, justifies the author in feeling that 



it is by all means the preferable method for use 
in the dental office. 

With the head thus supported, as shown in Pig. 
41. the rays are directed from the opposite side 

of the hoad, and therefore must pass through the 
entire face or skull in transit. The question nat- 

Fig. 40. 
The arrangement of the ap] - reparatory to seating the patient. 

urally arises, how is this to be accomplished with- 
out superimposing the shadows of one side upon 
the shadows of the other side, and thereby pro- 
ducing a chaotic result. 

For instance, let us suppose that we wish to 
obtain a radiograph of the left side of the upper 



and lower jaws extending from the cuspid region 
in front to the angle of the jaw behind, and from 
the floor of the orbit above to the inferior margin 
of the mandible below. If we are to get a cor- 
rect shadowgraphic representation of this area, 
it should be free from the shadows of the oppo- 

Fig. 41. 

The patient seated and the apparatus arranged for making a radiograph 
of the left side. The comfortable position of the patient renders it an easy 
matter to remain perfectly quiet. 

site side, and this can only be accomplished by 
directing the rays in such a manner that they will 
miss the areas not desired and will pass through 
those we wish to record. 

In accomplishing this, we must take into con- 


sideration two structures, viz. : the spine and the 
ascending ramus of the mandible (on the right 
side in this instance as the left side is to be radio- 
graphed) and cause the rays to pass in through 
this opening and thereby reach the desired area. 
The way in which this is accomplished is shown 
in Fig. 42, A and B, and Fig. 43, A and B. 

An important factor in accomplishing this is 
the position in which the patient's head is held 
as it is pressed against the plate. Held in the 
manner shown, the rays can be made to pass in 
between the ascending ramus of the mandible and 
the spine, and can pass in at approximately a per- 
pendicular direction to the long axis of the teeth 
and the plate, giving correct shadow lengths upon 
the plate. Fig. 44 shows a radiograph made by 
using this technic. 

If this rule is disregarded and the rays passed 
through the structures, as shown in Fig. 45, A 
and B, the shadows of the opposite side will be 
superimposed upon the shadows of the structures 
desired, and a chaotic result produced. The re- 
sult of such technic is shown in Fig. 46. 

In a similar manner as shown in Figs. 42 and 
43, with slight adjustments in the position of the 
plate, the head and the tube, the areas in the up- 
per and lower jaws extending from the median 
line to the first premolars, and from the nose 
above to the inferior margin of the mandible be- 
low, can be radiographed (Fig. 47, A and B). 
Likewise the structures at the median line includ- 



Fig. 42-A. 

Fig. 42-B. 

Technic for left side. M-L, median line; S, the spine; A, ascending ramus 
and angle of lower jaw; P-F, plate or film. 


Fig. 43-A. 

Fig. 43-B. 

Technic for right side. M-L, median line; S, the spine; A, ascending 
and angle of lower jaw; P-F, plate or film. 



Fig. 44. 

ing the incisors, both above and below, the an- 
terior portions of the mandible and maxilla, the 
nasal cavity and its accessory sinuses, may be 
radiographed by passing the rays directly through 
the skull, as shown in Figs. 48 and 49. In this in- 


Fig. 45-A. 

Fig. 45-B. 

Incorrect technic. The shadows of both sides will be imposed upon 
the plate. 


Fig. 46. 

The result of incorrect technic. This is a radiograph of the same subject 
as shown in Fig. 44. 

stance, the shadow of the spine will be superim- 
posed upon the dental structures, but owing to 
the fact that it is so far removed from the plate, 
its shadow does not interfere seriously. It is im- 


Fig. 47-A. 

Fig. 47-B. 

The areas in the upper and lower jaws extending from the median line 
to the first premolar can be radiographed by utilizing this technic. A, Tech- 
tlic for left side; B, Technic for right side. 


portant, in making these pictures, to have the pa- 
tient's head supported in such a manner that it 
can be held still for a longer period than is re- 
quired in making the exposures of the other areas 

When ready to make the exposure for extra- 
oral radiographs, the apparatus is arranged with 
the anode of the tube about twenty inches from 

The structures at the median line including the incisors, both above and 
below, may be secured in this way. 

the plate. The patient is instructed to keep the 
mouth closed with the teeth together in their nat- 
ural occlusion. They should also be warned as to 
the approximate length of time the exposure will 
require, and that they must remain perfectly 
With the more powerful types of apparatus, 



extra-oral radiographs require but short ex- 
posures, but if an operator does not possess high 
power apparatus, he should not hesitate to use 
this method, as a patient properly seated and sup- 
ported, as shown in Fig. 41, can easily remain 

Fig. 49. 

In following the technic illustrated in Fig. 48 the patient's head should be 
supported by a bandage of gauze to insure perfect immobility. 

quiet for five or ten seconds, or perhaps even 
longer, should it be necessary. 

In making a complete radiographic examina- 
tion of the teeth, the maxilla and mandible, the 
author suggests the following procedure. Extra- 
oral radiographs should be made of each side, 
using the technic illustrated in Figs. 42, 43 and 


47. This would mean two plates for each side. 
Then by the use of the intra-oral films, the region 
lying between the cuspids both above and below, 
should be radiographed. These plates and films 
should then be developed and examined. If the 
procedure has been carried out with due regard 
for all the elements involved, the result should 
constitute a general radiographic survey of the 
teeth, the maxilla and the mandible. Should any 
of the plates or films exposed fail to result in 
good radiographs, additional exposures should be 
made as nothing but good radiographs should be 
depended upon for diagnosis. 

It is sometimes advisable after making a com- 
plete radiographic examination by the method 
just advocated, "to check up" the findings of ex- 
tra-oral radiographs by the use of the intra-oral 
films. For instance, suppose a large plate shows 
what appears to be an abscess upon the root of 
an upper bicuspid or molar tooth. An intra-oral 
radiograph of this particular area will often set- 
tle any doubts, as a higher degree of detail can 
often be obtained by concentrating upon the small 
area in question. 

The author would not wish to imply by the pre- 
ceding remarks upon technic, that the few rules 
enumerated constitute a safe and never failing 
means of producing good radiographs. There are 
many points to be considered which cannot be in- 
cluded in so limited a text, but which must be 
learned in the school of experience, such as the 


necessary variations from the given rules of tech- 
nic because of anatomic variations in the dental 
and oral structures of patients. Therefore the 
rules of technic which have been presented must 
be accepted only in the light of principles. 




Successful radiography depends upon a se- 
quence of operations, each of which must be car- 
ried out with scientific accuracy. These steps, 
upon which the finished product depends, may be 
enumerated as follows : 

1st — Correct teclmic of position. 

2nd — Proper tube and current conditions. 

3rd — Correct exposure and development of 
plates and films. 

It would be difficult to determine which of these 
steps is the most important ; in fact, they are all 
so important that a radiograph is a success or 
failure in accordance with the degree of accuracy 
with which each is carried out. In the preceding 
chapter, the actual teclmic of radiography, so far 
as the arrangement of apparatus is concerned 
and its relative position to the patient and the 
plate (or film), has been discussed. We will 
therefore proceed to the next factor for considera- 

Proper Tube and Current Conditions 
The character of the x-rays produced in a tube 
depends upon the degree of its vacuum and the 



current which passes through it. We know that 
the x-rays are produced by the cathode stream 
striking the anode or target, and that this cath- 
ode stream (Fig. 25 M) is generated by the flow 
of the current in the tube. The velocity of the 
cathode stream depends upon the voltage of the 
current entering the tube, therefore the higher 
the voltage, the faster the cathode stream travels, 
and the more intense or penetrating are the x- 
rays produced. The quantity of x-rays produced 
depends upon the milliamperage of the current. 
In considering the role enacted by the voltage 
and milliamperage in the x-ray production, we 
have assumed that the tube is exhausted to a high 
degree of vacuum, for the degree of vacuum de- 
termines to a large extent, the value of the other 
two factors. The degree of vacuum of a tube is 
designated as high, medium or low, a "high tube" 
being one in which the vacuum is well nigh com- 
plete; in a "medium tube" the vacuum is less 
complete, while a "low tube" is one in which the 
vacuum is far from complete. 

For dental radiography a fairly high tube is 
indicated, as with such a tube x-rays may be pro- 
duced having a degree of penetration sufficient to 
pass through the oral structures and produce the 
desired effect upon the emulsion of the plate or 

When a current of high voltage is passed 
through such a tube, it should light up in a char- 
acteristic manner forming two hemispheres which 



have a definite line of demarcation. The hemi- 
sphere in front of the target which is the active 
hemisphere, is evident by a florescence deep 
apple green in color, while the other hemisphere 
should be evident by a lack of greenish light. 

To Determine the Vacuum of a Tube 

The comparative degree of vacuum of a tube 
can be determined in the following manner : Con- 


Fig. 50. 

nect the tube to the x-ray machine as shown in 
Fig. 50. See that the third terminal (S') is 
moved well away from the negative terminal (#), 
or better still, disconnect the wire running to the 
regulating chamber (R). Now, move the sliding 
rods (B and D) of the secondary spark gap, to- 


ward each other until they are about three inches 
apart, and start the current. Unless the tube is 
low, the current will jump the spark gap instead 
of passing through the tube. If the tube resists 
the current and causes it to jump the spark gap, 
it is said to have "backed up" three inches of 
spark. Thus a "low tube" will back up two or 
three inches of spark, a "medium tube" five or 
six inches, while a high tube will back up six or 
eight inches. In fact, the vacuum of a tube may 
be so great that only the most powerful x-ray 
machines will operate it. Such a tube, however, 
is not useful for dental radiography. 

The vacuum of a tube may also be determined 
by the use of an instrument known as a milUam- 
peremeter. This instrument which is usually an 
accessory of either the induction coil or trans- 
former, is connected in circuit with the tube, and 
measures the current passing through the tube. 
With a "low tube" the milliamperemeter will 
show a reading of 15 to 18, while with a "medium 
tube" the reading will be from 10 to 12, and with 
a "high tube" the milliampere will register 5 or 

Relative Merits of Low, Medium and 
High Tubes 

A "low tube" in operation under average cur- 
rent conditions gives a clear sharp hemisphere 
of pale greenish light in front of the target, with 
usually a trace of bluish light in the region of 


the assistant anode. If the tube is very low, the 
cathode stream shows blue, and there is a bluish 
light back of the active hemisphere. Such a tube 
will not do good radiographic work as the x-rays 
produced by it are lacking in penetration. 

A "medium tube" gives a clear, sharp hemi- 
sphere of light greenish color, and there is an ab- 
sence of bluish light back of the target. The rays 
emanating from such a tube are more penetrat- 
ing than those from the "low tube," but are not 
as well suited for "bone radiography" as those 
which come from a tube fairly high in vacuum. 
When such a tube is operating, it gives a clear 
sharp hemisphere deep apple green in color, with 
a lack of greenish light back of the target. The 
x-rays emanating from such a tube are of a de- 
gree of penetration which is best suited for bone 
radiography, for they penetrate and pass through 
the soft tissues and to a sufficient degree through 
the bone structure to give good contrast. 

It is very important that the vacuum of such 
a tube be kept uniform, for if it gets low the 
power of penetration of the rays is decreased, 
and on the other hand if the vacuum gets too high, 
the penetrating power of the rays will be in- 
creased, with the result that they will penetrate 
through the bone structure as easily as the soft 
tissues. Consequently, unless very short expos- 
ures are given, there will be little if any contrast, 
and the plate will be dark and hazy. 


Regulating the Tube 

Prior to seating and arranging the patient, the 
tube should be tested out and any needed change 
in its vacuum effected. This is easily accom- 
plished by utilizing the third terminal of the x- 
ray machine. The tube should be connected to 
the machine as shown in Fig. 50. The terminals 
of the regulating spark gap (S', S) should be 
placed about four inches apart, and the current 
(of correct working strength) turned on for an 
instant. If a line of sparks jump between S' and 
S, it shows the vacuum of the tube is too high. In 
this event the regulating spark gap (S , S) should 
be reduced to about two inches, and a small 
amount of current turned on. This weaker cur- 
rent will pass across the spark gap S', 8, travel 
down the wire connected to the regulating cham- 
ber and by heating the asbestos (impregnated 
Avith chemicals) will liberate enough gas to re- 
duce the vacuum. Unless the tube is very high, 
a few seconds will suffice to reduce it to the 
vacuum desired. To be sure the vacuum is right, 
the regulating spark gap (S', S) should be wid- 
ened to about four inches, and the desired work- 
ing current again passed through the tube for an 
instant. If the tube lights up with a clear sharp 
active hemisphere deep apple green in color with 
a lack of greenish light back of the target, you 
then know it is ready for work. 

If an x-ray machine is not equipped with a 
third terminal, the same results in regulating the 


tube may be effected by using the regulating ad- 
juster (Fig. 51), the end of which can be placed 
at the desired distances from negative wire near 
its point of attachment to the tube. The tube 
may also be lowered by attaching the negative 
wire directly to the regulating chamber and pass- 
ing a small amount of current through the cir- 

These manipulations should be carried out 

A — Anode. 
U- -Assistant Anode 
C— Cathode 
D— RcKuIatint? 
T— Regulating Ad- 

G— Hemisphete 

H — Connection 

I- Assistant Anode 

K— Anode ( ap 

I Cathode Cap 

M— Cathode Stream 
N— Focal Point 

Fig. 51. 

iviih the greatest caution, for a tube is an ex- 
tremely delicate and sensitive piece of apparatus 
and will not stand abuse. 

A careless operator can quite easily reduce the 
vacuum to such a degree that the tube is useless. 
Such a tube has a purple appearance when the 
current is passed through it. If such a tube has 
not been too greatly abused, it will often regain 
its vacuum if given a rest. If this does not bring 
the vacuum up, it can often be brought back in 


the following way: The spiral spring (Fig. 51) 
connecting the anode and assistant anode, should 
be removed and the positive wire from the ma- 
chine attached to the assistant anode (7). The 
negative wire is attached as usual (at L) and a 
light current is run through the tube for a min- 
ute or two at a time. If this is done once or twice 
a day for several days, the vacuum will usually 
come up. Any increase in vacuum will be indi- 
cated by the milliampere readings dropping off, 
or by the increased length of spark gap the tube 
will "back up." 

If a tube does not respond to this treatment, 
but continues to be purple while operating, it indi- 
cates that it is practically non-vacuous or "punc- 
itured." It is then useless and should be sent 
back to the manufacturer for repairs. In the 
event a tube is "completely punctured, " the cur- 
rent in passing through it simply jumps the gap 
between the anode and cathode, and is evident as 
a line of white sparks. 

One tube complication not yet mentioned is 
sometimes encountered in the use of induction 
coils. This is known as "inverse in the tube," 
and is the result of the presence of inverse cur- 
rent (current in the wrong direction) in the sec- 
ondary circuit of the coil. "Inverse" is evident 
in the tube by the appearance of rings of light 
back of, and usually running at an angle to the 
active hemisphere, or by a fullness of greenish 


light back of the active hemisphere, with rings 
about the assistant anode. 

Inverse current in a tube will generate second- 
ary rays which have the tendency to make the 
outline of the image on the plate hazy or "less 
sharp," as these rays are produced in the tube 
elsewhere than at a focal point on the target. It 
also produces heat in the tube which lowers the 
vacuum and hence lessens the penetration of the 
rays coming from it. 

' i Inverse ' ' in the tube can usually be controlled 
or prevented by the use of "a multiple spark 
gap" or "a valve tube" arranged in series with 
the x-ray tube, and by using a tube which is fairly 
high in vacuum. If it still persists after these 
precautions are taken, it indicates an imperfect 
adjustment of the induction coil or some of its ac- 

All manufacturers of x-ray tubes furnish full 
instructions as to the care of and manner of us- 
ing x-ray tubes. These instructions should be 
carefully read and explicitly followed. 

In order that uniform results may be obtained, 
it is advisable to always use the tube at the same 
vacuum, with the same amount of current. The 
proper "working current" may be determined in 
the following way: With the tube disconnected, 
set the sliding rods (B and D of Fig. 50) of the 
machine about six inches apart. Then start the 
current in the machine, and beginning with a 
low current increase it until a fat fuzzy "cater- 


pillar spark" is produced across the spark gap. 
As soon as this spark or discharge appears, the 
switch should be pulled out, hut the rheostat or 
other controlling apparatus left as it was when 
the spark appeared, so that when the tube is con- 
nected, the proper working current will come from 
the machine. 

The tube should then be connected up and given 
a trial. If it is not too high in vacuum, it should 
take the current, or in the event it is too high, it 
will "back up" the spark, and the discharge in- 
stead of passing through the tube will jump the 
gap. If the tube requires regulating it can be 
done by the methods before described. 

With the working current and vacuum estab- 
lished, it is a good idea to separate the sliding 
rods on the machine to at least eight inches, to 
insure against the tube backing up the current, 
for in the event the tube should start going up 
during the time the exposure is being made, the 
startling noise made by the discharge jumping 
the gap, may cause the patient to move and there- 
by blur the radiograph. If several exposures of 
five or ten seconds each are made, the tube should 
be given sufficient rest between exposures so that 
it will not heat up. This is important. 

With proper tube and current conditions, the 
length of time required for the exposure will de- 
pend upon the type of x-ray machine used, and 
the thickness and density of the parts to be radi- 
ographed, varying with different patients accord- 
ing to age and structural make up. 


Correct Exposure and Development of X-Ray 
Plates and Films 

X-ray plates and films differ from those used 
in ordinary photography in that their emulsion 
is more sensitive and better adapted to record 
the shadows produced by the x-ray. Therefore 
they should always he used in preference to ordi- 
nary plates and films. 

The same general photographic rules apply to 
x-ray plates and films as apply to the ordinary 
kind, except perhaps that they demand a greater 
degree of accuracy and care throughout the proc- 
ess of exposure and development, if the very best 
results are to be obtained. 

X-Ray Plates 

X-ray plates are supplied by the manufacturers, 
packed in light-proof boxes containing one dozen 
plates. They are obtainable in any desired size, 
but for dental and oral radiography, a 5x7 plate 
is large enough. If stored in the laboratory, they 
should be kept in a lead-lined box prior to their 
preparation for exposure, or they will become 
"fogged," as light-proof boxes offer no protec- 
tion whatever from the x-ray. 

In their preparation for exposure, each plate 
is placed in two light-proof envelopes, one of 
which is black and the other red or orange in 
color. Such envelopes are furnished by plate 
manufacturers and are obtainable in the desired 


size. The transference of the plate from its orig- 
inal box to the envelopes must, of course, only be 
done in the photographic dark room. The plate 
is first slipped into the smaller envelope which is 
usually the black one, with the emulsion side of 
the plate facing the smooth side of the envelope 
(the side free from seams or overlapping edges). 
The envelope containing the plate is then placed 
in the larger or yellow envelope, flap-end first, 
with the smooth side of the inner envelope fac- 
ing the smooth side of the onter one. Plates pre- 
pared in this way are then ready for exposure and 
can be placed back in the lead-lined box until 

In "loading these envelopes," care should be 
taken lest the emulsion of the plate become 
scratched, as scratches even though they be very 
slight will often curtail the value of the finished 

It is not advisable to keep large quantities of 
plates loaded in envelopes, unless they are to be 
used within a few days, as the contact of the pa- 
per with the emulsion will in time affect it ad- 

All "brands" of x-ray plates are not the same, 
therefore if the best results are obtained in us- 
ing any particular kind, they must be handled in 
strict accordance with the manufacturers' in- 
structions. For dental and oral radiography, a 
plate should be fairly rapid (that is, it should 
not require a long exposure), give a high degree 


of detail and good contrast, and should be uni- 
form in its reaction to the x-ray. 

X-Ray Films 

In making intra-oral radiographs, a film is 
preferable to a plate as it is flexible and there- 
fore can be more easily adapted to the inside of 
the mouth. These films are obtainable in several 
convenient sizes, wrapped in light-proof and 
damp-proof coverings ready for exposure. Like 
plates they should be kept in a lead-lined box for 

With these " dental films" as they are called, 
you have the choice of two different emulsions, 
onj8 of which is much more "rapid" than the 

The "rapid" or "fast film" requires only 
about one-fourth or one-third as long an expos- 
ure as the "regular" or "slow film," and there- 
fore is an advantage to the radiographer who 
uses one of the less powerful types of x-ray ma- 
chines. However, such a film does not have as 
much latitude as the slow film, and is therefore 
more apt to be over-exposed. If properly ex- 
posed, either one will give satisfactory results. 

"When arranging a plate or film for exposure, 
the emulsion side should lie next to the structures 
being radiographed. If this rule is systemati- 
cally followed, it is an easy matter to identify 
radiographs, i.e., whether they represent struc- 
tures on the right or left side of the median line. 


The process of "development" of either plates 
or films may be briefly described as follows : At 
a convenient time following the "exposure," the 
plate or plates (or films) are taken into the 
"darkroom." Such a room has all white light 
excluded from it, and is illuminated only by a 
so-called ' ' ruby light ' ' or darkroom lantern. The 
darkroom should be supplied with a shelf or table 
about two and a half feet wide and three feet 
long placed at ordinary table height from the 
floor, so that the operator may sit upon a stool 
while at work. Upon this shelf there should be 
four trays, one for "the developing solution," 
one for the "fixing bath," and the other two for 
water. "Where a darkroom is supplied with run- 
ning water and a sink, only three trays are nec- 

With all light excluded from the room except 
the ruby light coming from the darkroom lan- 
tern, the plate (or film) is taken out of its envel- 
ope and immersed emulsion side up in the devel- 
oping solution. In order to insure a uniform ac- 
tion by the developer, the tray should be fre- 
quently rocked with a gentle motion. If the plate 



(or film) lias been properly exposed, development 
should be complete in about five minutes (al- 
though the time varies with different formulae). 

The plate or film is then removed from the de- 
veloper and placed in a tray of water to thor- 
oughly wash the developing solution from it. 
This, of course, requires but a moment, and it 
is then immersed in the " fixing bath," keeping 
the emulsion side up. As soon as the plate has 
been in the fixing bath a few seconds, the dark- 
room door may be opened and light admitted 
without injurious effects. However, the plate (or 
film) must still remain in the " fixing bath" un- 
til it has "cleared" (until all milkiness is gone 
from the back of the plate), which will usually 
require from five to ten minutes. In fact, it is 
better to let it "f^" for at least five minutes 
longer than is required for it to become clear. 

When the fixing process is complete, the plate 
must be placed in water and thoroughly washed 
to remove all the fixing solution from it. This 
can be accomplished by washing it in several 
changes of water, or better still, place it in a basin 
or tray of cold " running water" for ten or fif- 
teen minutes. 

"When the washing process is complete, the 
emulsion side of the plate or film should be gen- 
tly rubbed with a clean piece of wet cotton, hold- 
ing the plate (or film) under a cold water faucet 
during the act. The developed radiograph is then 


ready to dry. Plates should be stood on edge or 
placed in a suitable rack so that nothing will come 
in contact with the emulsion side, and left until 
perfectly dry. Films may be pinned to the edge 
of a shelf, or secured to a line with suitable clips. 
The drying process should take place in a room 
free from dust or soot, for these will prove in- 
jurious to the drying emulsion. 

The size of the trays used in the darkroom will 
depend upon the number of plates or films which 
are to be carried through the developing process 
at a time. For plates, the author uses trays 8x10 
inches in size. With such trays two 5x7 plates 
can be carried through at a time. Where a large 
number of plates are being developed, additional 
trays can be used and if necessary "tanks" capa- 
ble of holding a dozen plates, utilized in the fix- 
ing or washing process. In developing "dental 
films," small trays will be found convenient, and 
unless a large number are to be developed at a 
time, a 4x5 or 5x7 tray will be large enough. 

Trays should be labeled according to the pur- 
pose for which they are to be used, and used for 
that purpose only. That is, developing trays 
should be used for developer only, and "fixing 
trays" only for the fixing bath, if troublesome 
chemical reactions are to be avoided. 

Any one of several good formulae may be used 
in the "developing" and "fixing" process. The 


following has given satisfactory results in the 
hands of the author, and is easily prepared : 


Water (distilled) 









Sodium sulphite (dry) 



Sodium carbonate (dry) 



Potassium bromide 



Fixing Bath 

Solution A: 

Water (distilled) 



Hyposulphite of soda 



Solution B : 

Water (distilled) 



Chrome alum 



Sodium sulphite (dry) 



Solution C: 

Water (distilled) 



Sulphuric acid (C.P.) 



Add C to B (when cold) and the mixed solu- 

tions to A. 

If the best results are to be obtained in develop- 
ing, the temperature of the solution should be 
kept between 65° and 75° F. If the temperature 
gets much over 75°, the plate will develop too 
fast, while if the temperature goes much below 
65°, development will be retarded. 

It is a mistake to try to develop a large number 
of plates with the same mixture of developer, for 


after it has developed a half dozen plates, it will 
become weak and not give the best results. 
Therefore, do not hesitate to use plenty of fresh 
developer if you expect to get satisfactory re- 

The same rule applies to the "fixing solution." 
It must be fresh and clean to give good results. 

Under proper tube and current conditions, and 
with correct length of exposure, a plate should 
require about five minutes for its development. 
An over exposed plate will not require so long, 
while an underexposed plate will require a longer 

To get the most out of a plate, it should be de- 
veloped until fairly dense, that is, until it is about 
the same color on each side. If after it has 
cleared in the fixing bath, it appears too dark or 
dense, you know that it has been "overexposed." 
Therefore in making subsequent exposures de- 
crease the length of exposure. If, upon clearing, 
the image on the plate is faint and indistinct, you 
have reason to think it has been underexposed. 
Therefore, increase the length of exposure. 

By keeping the tube and current conditions 
right, the approximate length of exposure for any 
given case is easily determined by the operator, 
after a little experience. As stated before, this 
will depend upon the type of x-ray machine used, 
the thickness and density of the parts to be radi- 
ographed, and the age and structural make up of 
the patient. 



The ability to correctly interpret dental and 
oral radiographs is an accomplishment which ev- 
ery dentist should possess. In fact, it should be 
viewed not only in the light of an accomplishment, 
but as a requisite of modern dentistry. It is to 
be acquired by practical experience which must 
have for its foundation, first, a thorough knoivl- 
eclge of the anatomy of the parts involved; sec- 
ond, a familiarity with the appearance in the radi- 
ograph of the dental and oral structures under 
normal conditions; and, third, a knowledge of the 
pathological conditions ivhich may develop in 
'these structures, and the character of the ana- 
tomical changes ivhich they bring about. 

We . should keep in mind the fact that radio- 
graphs are shadow pictures, and that the effect 
produced by the x-ray upon the photographic 
plate is but a shadowgraphic representation of 
the tissues through which the rays have passed. 
As this ray penetrates all matter in inverse ratio 
to its mass or density, the shadow picture which 
is left upon the photographic plate is simply a 
record of the varying density of the tissues 
through which the rays have penetrated. 

The x-ray is particularly applicable to the den- 



tal and oral structures, owing to the fact that 
these structures differ sufficiently in degree of 
density to 'permit of their appearing in a char- 
acteristic manner upon the photographic plate. 
For instance, it will be noted upon the examina- 
tion of a dental radiograph, that metallic fillings, 
if they are present, appear as white masses, and 
root fillings as somewhat less white lines. The 
enamel and dentin are next in density, while root 
canals show plainly as dark channels in the den- 
tin, and the alveolar process and maxillae show 
their fine uniform cancellous structure in various 
degrees of density depending upon their thick- 

Because the structures within the field of our 
specialty have a characteristic appearance under 
normal conditions, any alterations or change in 
these structures is at once evident upon the plate, 
thus affording us a means of studying intravitam 
the gross pathology of the structures of the oral 

Examination of Radiographs 

Dentists often underestimate the value of radi- 
ographs because their opinion is based upon their 
appearance either in halftone engravings or af- 
ter their transference upon lantern slides. As 
such they should never be judged, as much of 
their diagnostic value is lost when reduced to 
this state. 

The original negative itself should be exam- 
ined carefully and in a proper light. This is best 


accomplished by the use of an 'illuminating'' 
boN or cabinet. Such a cabinet should contain 
several electric lamps, and the current entering 
these lamps should be controlled by a rheostat, 
or some other means, by which the intensity of 
the light may be changed at the will of the oper- 
ator, causing it to start with a very dim light and 
gradually increase until a brilliant illumination 
is produced and vice versa. The face of this cab- 
inet should be covered with ground glass so that 
the light will be free from shadows and equally 
distributed. An opaque mat with an opening the 
exact size of the plate under examination, should 
be placed over the ground glass so that the vision 
is not distributed by the light escaping from 
around the edge of the plate or film. Only by us- 
ing such a cabinet can radiographs be examined 
and interpreted to the very greatest advantage. 

To one who has never seen a negative illumi- 
nated in this manner, the effect is almost startling 
in its beauty. As the x-ray negative is a trans- 
parency, a dim light behind it will bring out one 
set of shadows to their greatest clearness ; an in- 
crease in the light will show forth still other ef- 
fects, while a still greater illumination will bring 
out the more dense portions of the negative, and 
in this way by varying the light in the illuminat- 
ing box, each portion of the negative may be 
studied under a degree of light to bring out the 
maximum amount of detail. 

Xow with a print or lantern slide one can ex- 



amine the field from only a one light aspect, and 
oftentimes in order to secure any degree of de- 
tail in the lighter or less dense areas, it will be 
found that the dense areas must be printed al- 
most to an inky blackness. It should be obvious. 

1 / 

1 8PH 

h£~ 1 

Fig. 52. 

This radiograph shows an impacted upper third molar. The outline of the 
antrum is also plainly visible above the molars and bicuspids. 

therefore, that a single-phase print, or a nega- 
tive, examined under ordinary conditions, cannot 
approach the various and comprehensive effects 
which are brought out by means of an illuminat- 
ing: cabinet. 



In examining intra-oral radiographs, it is an 
advantage to place them in a film mount which 
will hold them securely and render it unnecessary 
to view them while being held between the fingers. 

Fig. 53. 

A cuspid tooth lying against the anterior wall of the antrum. It will be 
noted that the cuspid is inverted in its position. 

Such a "mount" should preferably be made of 
celluloid with one side clear and the other side 
dull, which allows the light transmitted to be of 



the same character as that coming through ground 

In examining negatives, we should bear in mind 
the fact that very dense tissues are characterised 
by white areas, while less dense tissues appear 
darker, and the absence of tissue is indicated by 
blackness. To avoid confusion, we should remem- 
ber that in prints and lantern slides this color 
spectacle is reversed. 

Fig. 54. 

A supernumerary second bicuspid. Upon the extraction of the second 
bicuspid in place at the time the radiograph was made the "supernumerary" 
erupted, and was found to be typical in size and form. 

Assuming now that we are familiar with the 
normal appearance of the dental structures un- 
der the x-ray, let us now consider some of the 
variations from their normal appearance which 
are found in the presence of pathological condi- 

As a tooth is much more dense than the bony 
structures of the jaw, any anomaly of form, size 



or position in the jaws is easily discernible even 
though it occupy a position far from what might 
he expected, as for instance, in the case of im- 

Fig. 55. 

A radiograph to determine the state of dentition of the right side in the 
mouth of a child eleven years old. The developing second molars are 
shown, likewise the upper second bicuspid, and the lower first bicuspid about 
to erupt. It will be' noted that the lower second deciduous molar has no 
successor, nor is there an upper first bicuspid present in the jaw. 

pacted molars, teeth in the antrum, etc. (See 
Figs. 52, 53 and 54.) 

Likewise and for the same reason the presence 
in or absence from the jaws of successors of the 




Fig. 57. 

A very large alveolar abscess is visible below the mesial root of a 
lower molar. 

Fig. 58. 

An alveolar abscess involving the roots of an upper central incisor and 
lateral incisor. No root canal fillings are present in either tooth. 



deciduous teeth can easily be determined, as 
shown in Figs. 55 and 56. 

Fractured roots or fractures of the hone even 

Fig. 59. 

An abscess is visible between the central and lateral incisors. Its origin 
could be due to either tooth or perhaps to both. 

Fig. 60. 

There is evidence of a small alveolar abscess about the apex of the root 
of the first bicuspid, while a larger one is shown to exist about the root of 
the second bicuspid. 

without displacement are often discernible at the 

line of fracture, owing to the fact that the line of 


fracture offers less resistance to the penetration 
of the rays and therefore is apparent upon the 
plate as a dark line. 

Where an abscess takes place in the alveolar 

Fig. 61. 

Alveolar abscesses above two bicuspid teeth. The relationship of the 
abscess areas to the antrum is also shown. 

Fig. 62. 

Large alveolar abscess, chronic in character, about the apex of upper 
first bicuspid. 

process, there is always an accompanying destruc- 
tion of the cancellous bone tissue. Knowing that 
the absence of tissue is indicated upon the plate 
by a very dark or black area, such an area would 


indicate an alveolar abscess. "In fact, where 
these dark areas are found in the alveolar proc- 
ess, and are not natural cavities, such as the an- 
trum, or the nasal cavities, or such well denned 

Fig. 63. 

Large alveolar abscesses emanating from the upper lateral incisor and 
extending to the adjacent central incisor and cuspid. 

Fig. 64. 

Chronic alveolar abscess cystic in character, above an upper lateral incisor. 
Root filling material forced through the end of the root is plainly visible. 

nerve openings as the mental foramina, and where 
they are markedly circumscribed, that is, having 
a distinct and abrupt line of demarcation between 
the dark area and its surrounding tissues, we can 



in nearly every case, even if a clinical history be 
lacking, make the positive diagnosis of alveolar 
abscess." (See Figs. 57, 58, 59, 60, 61, 62, 63, 64 
and 65.) 

Necrosis likewise appears upon the plate as a 
dark area, bnt differs in a characteristic way 
from the ordinary alveolar abscess in that it is 

Ki 1 

I ■ JL \ I 

^L w^W^^ A 

! c 

L m* X 


Fig. 65. 

A shows an upper bicuspid tooth with an alveolar abscess at its root 
apex. It will be noted that the root canal is improperly filled. B shows 
the same tooth about two months after it was treated and the root canal 
properly filled. The rarified area about the apex has greatly decreased in 
size. C shows the same tooth about six weeks later. The abscess area 
has entirely disappeared and the bone structure about the apex appears to 
be normal. 

not circumscribed, namely, that there is not a dis- 
tinct and abrupt line of demarcation betiveen the 


dark area and its surrounding tissue, as is the 
case with the circumscribed infections, but the 
area gradually shades off from dark into light, 

Fig. 66. 

A necrotic area lying below a lower cuspid. It will be noted that there 
is not a distinct and abrupt line of demarcation between the light area and 
its surrounding tissue as is the case with alveolar abscesses, but the area 
gradually shades off from light into dark. 

portraying the progressive characteristics of this 
disease. (See Figs. 66 and 67.) 

The different tilling materials vary but little 



in the relative graduation of their shadows. Oxy- 
chloride, gutta-percha, and cement have about the 
same density, and when used as root rilling ma- 
terials, are plainly visible as light lines. Because 
they differ in density from cementum and den- 
tin, the extent to which they have been intro- 
duced into the root canals is easily discernible. 

Fig. 67. 
An area of necrosis about the roots of a lower first molar. 

Broken-off broaches and other instruments, or 
small wires introduced into root canals to deter- 
mine their length or the extent to which they have 
been opened, because of their great density, ap- 
pear very white and are easily differentiated from 
root-canal fillings or tooth structure. (Figs. 68 
and 69.) 
Where a destructive process has ensued in the 



peridental membrane, or in the bony Avail of the 
alveolus (pyorrhea pockets) and is present on 
the mesial or distal side of a tooth, these condi- 

Fig. 68. 

Small wires introduced into root canals to determine their length or 
the extent to which they have been opened, are easily differentiated from 
root canal fillings or tooth structure. 

Fig. 69. 

Root canal filling material forced beyond the root apex of an upper 
second bicuspid. 

tions appear npon the plate as dark areas owing 
to the fact that the rays pass through them more 
easily, and effect the emulsion of the plate to a 


Fig. 70. 

An abscess involving the pericemental and alveolar tissues about an 
upper first bicuspid. 

Fig. 71. 
An osteo-sarcoma of the mandible. 


greater degree than if normal bone structure is 
present. The approximate extent of the destruc- 
tive process is therefore easily determined. (Fig. 

Cysts and tumors of the maxilla or mandible, 
owing to the fact that the character of the changes 
they bring about renders the areas involved less 
dense, their extent is visible upon the plate as a 
dark area. (Fig. 71.) 

In seeking out the various anomalies and path- 
ological conditions to which the teeth and oral 
structures are subject, we should not be misled 
by indefinite shadows upon x-ray plates. The 
very nature of these structures, their gross as 
well as minute anatomy, renders them somewhat 
difficult to radiograph, and necessitates a refine- 
ment of technic greater than that demanded with 
most of the other portions of the human anatomy. 
Therefore, only radiographs made in accordance 
with a definite and exacting technic shoidd be re- 
lied upon for diagnosis. If a doubt exists in any 
given instance, an additional or even several more 
exposures shoidd be made, so that any conclusion 
reached will be founded upon definite evidence. 



Almost invariably when any phase of x-ray 
work is discussed someone raises the query as to 
the dangers connected with it and the injuries 
resulting from its use. In fact, the impression is 
quite broadcast among the laity, and to a degree 
among the profession, that the x-ray is a danger- 
ous agent and as such should only be employed 
in cases of dire emergency. 

This impression, erroneous as we know it to be 
for the most part, gained credence as a result 
of the first few years' use of the x-ray, during 
which period its dangers were not suspected nor 
the laws governing its use well understood. Dur- 
ing this period a sufficient number of patients and 
operators were injured so that, notwithstanding 
the fact that with our present knowledge of the 
subject and with the marked improvement in x- 
ray apparatus these accidents are no longer nec- 
essary, the early impression still prevails to a 
certain extent. 

In order that we may not underestimate the 
dangers of this valuable agent and consider light- 
ly our responsibility in using it, we will now con- 
sider the character of injuries possible through 
its misuse. 



We should bear in mind the fact that the x-ray 

in medicine serves a double purpose. It is used 
as a diagnostic agent, that is in making radio- 
graphs and florescopic examinations, and as a 
therapeutic agent. In the latter capacity patients 
are subjected to repeated exposures, the length 
of which are very far in excess of that required 
in making radiographs. In fact the length of ex- 
posure in one average x-ray therapy treatment 
will more than out-total the necessary exposures 
to radiograph a half dozen patients for diagnos- 
tic purposes. Therefore, the responsibility of the 
x-ray therapist, and the danger connected with 
his work are far in excess of the man who limits 
his activities with the x-ray to radiography alone. 
Of the various ill effects attributed to the x- 
ray the so-called "x-ray burn" or dermatitis is 
the most common. This injury occurs in various 
degrees of severity, depending upon the amount 
of overexposure to which the one afflicted has 
been subjected, and is designated as "acute" and 

Acute X-Ray Dermatitis 

Acute x-ray dermatitis in its simplest form 
manifests itself in somewhat the same way as or- 
dinary sunburn. There is a slight pinkish ery- 
thema, dry in character, accompanied oftentimes 
by the sensation of tingling or burning. If x- 
ray exposures are continued this condition is aug- 
mented by the appearance of vesicles and the af- 


fected surface becomes moist or "weeping," and 
the patient has similar sensations as those pro- 
duced by any blistering burn. If exposures to the 
ray be discontinued at this stage, the affected 
area will slowly clear up with no permanent ill 
effect except perhaps a slight pigmentation. 

If the exposures be continued the next degree 
of dermatitis will ensue. The affected area be- 
comes an angry red in appearance, congestion is 
intense, and the surface is covered with a yellow- 
ish white necrotic membrane, which is epithelial 
in character. In fact, up to this point the con- 
nective tissue is not affected except for more or 
less swelling. This degree of dermatitis is ex- 
ceedingly slow in healing, months being required 
for the necrotic membrane to disappear, and when 
this has occurred it is followed by a horny epi- 
dermis which appears in spots over the area af- 
fected, eventually covering it. This new skin 
while quite smooth and natural looking is usually 
characterized by the absence of all hairs and fol- 

The most severe form of acute x-ray dermatitis 
is characterized by somewhat the same symptoms 
as those just described except that they are great- 
ly exaggerated. The degree of congestion is very 
great, the necrotic membrane extends deeper into 
the tissue,, necessitating the surgical removal of 
masses of dead tissue to prevent gangrene. This 
sloughing or necrotic area shows a strong ten- 
dency to spread and according to some authors is 


apt to become malignant. With such a dermatitis 
patients often suffer very intense pain. Injuries 
of this degree of intensity are exceedingly slow 
in healing, a number of years sometimes being 
necessary for the process of reconstruction. Even 
after it occurs the skin is not natural in appear- 
ance but hard and horny and covered in places 
with scar tissue. 

Chronic X-Ray Dermatitis 

After a person has been exposed to the x-ray a 
great many times covering a period of perhaps 
months or years, and has had one or more 
"burns" which were not allowed to heal before 
new effects were added by additional exposures, 
the dermatitis which results becomes "chronic." 
This chronic x-ray dermatitis is confined almost 
entirely to x-ray operators and others constantly 
associated with the x-ray. The hands because of 
their exposed position are most often the seat of 
this affection. The skin becomes thin and 
atrophic with red patches of a vascular nature, 
and there is usually an entire absence of all fol- 
licles and hair. Codman describes this condition 
as f ollows : "In the less pronounced forms the 
skin appears chapped and roughened, and the 
normal markings are destroyed; at the knuckles 
the folds of skin are swollen and stiff, while be- 
tween there is a peculiar dotting resembling 
small capillary hemorrhages. The nutrition of 
the nails is affected so that the longitudinal stria- 
tions become marked and the substance becomes 


brittle. If the process is more severe there is a 
formation of blebs, exfoliation of epidermis, and 
loss of nails. In the worst form the skin is en- 
tirely destroyed in places, the nails do not reap- 
pear and the tendons and joints are damaged.'' 
Another author states that "while the condi- 
tion in chronic forms of x-ray irritation is as a 
whole atrophic, there is usually a peculiar ten- 
dency to hyperkeratosis, which shows itself in in- 
creased horniness of the epidermis about the 
knuckles and in the formation of keratotic 
patches. In some cases this is very marked, so 
that the affected parts, usually the backs of the 
hands, have scattered over them many keratoses 
with or without inflamed bases. The appearance 
is very similar to that seen in senile keratosis 
where the patches are inflamed and have a ten- 
dency to epitheliomatons degeneration. The de- 
velopment of epitheliomas in these patches of x- 
ray keratosis has within the last few years been 
well established/' Carcinoma may also have its 
origin from the same source, in fact many x-ray 
operators who have failed to take the proper pre- 
cautions have been subject to this dreaded mal- 
ady, the hands being the parts most often af- 

Other 111 Effects 

In addition to the before described injuries 
there are still other ill effects attributed to the x- 
ray, such as loss of hair, sterility, and certain sys- 
temic effects. The loss of hair due to x-rav ex- 


posure is not to be regarded seriously, unless it 
is associated with a dermatitis of sufficient sever- 
ity to destroy the hair follicles, for unless this 
complication is present the hair comes back with- 
in five or six weeks. 

The x-ray has a deleterious effect upon devel- 
oping embryonic cells and can therefore be the 
cause of sterility in the male by destroying the 
spermatozoa, and in the female by the destruction 
of the primordial ovules. This condition is 
brought about by continued exposures, and x-ray 
operators are the ones usually affected. It is not 
accompanied by impotence, is temporary in dura- 
tion, and can be avoided entirely by adopting pro- 
tective measures. 

Eegarding the so-called injurious systemic ef- 
fects produced by the x-ray, too little evidence of 
a convincing character has yet been presented to 
really fasten the blame upon the x-ray for condi- 
tions other than those before enumerated. There- 
fore, until its guilt is scientifically substantiated 
we must not indict it for conditions which may be 
but a coincident with its use. 

Methods of Protection 

The evil effects of the x-ray can be entirely 
avoided by utilizing the protective measures af- 
forded in modern x-ray apparatus. Inasmuch as 
Read is impervious to the rays it can be used in 
different forms and in various pieces of apparatus 


in such a way as to control or confine the rays 
according to the will of the operator. 

Tube Shield 

The most essential piece of protective appa- 
ratus is the tube shield. This is constructed of 
leaded glass, there being a sufficient amount of 
lead salts incorporated in the glass to prevent or- 
dinary rays from passing through it. The sides 
extend up over the highest part of the tube and 
the opening at the top is often covered with a rub- 
ber cap, in which lead is also incorporated. At 
the bottom directly opposite the target of the 
tube an opening of the proper size is left to al- 
low the desired rays to pass out. The size of this 
opening may be controlled by interchangeable 
diaphragms of various sizes, which are con- 
structed of sheet lead about one-sixteenth of an 
inch in thickness. 

This apparatus is usually augmented by a com- 
pression cylinder, which is attached to the base 
of the tube shield, against or in contact with the 
lead diaphragm. Such a cylinder is usually con- 
structed of aluminum with a lead lining, is made 
in various lengths and diameters according to the 
character of the work it is to be used for, and 
serves the purpose of confining the rays coming 
through the diaphragm from the target of the 

These pieces of apparatus are usually integral 
parts of the modern tube stand, sold by all reli- 


able manufacturers of x-ray apparatus. It should 
be apparent to any one that with such apparatus, 
the only rays which leave the area of the tube are 
those which pass through the diaphragm and 
cylinder and are used upon the patient. In radi- 
ographic work these do not injure the patient, as 
the exposures are too short to produce ill effects, 
even if numerous exposures are necessary. 

On the other hand the radiographer who fails 
to use these protective measures, or who careless- 
ly places himself in the direct path of the rays 
will in time through the accumulative effect of 
the x-ray be very apt to reap as a result of his 
folly some of the dread injuries before described. 

Other Means of Protection 

In addition to the protective measures thus far 
described, there are other means which afford ad- 
ditional protection, and if a person is working 
constantly with the x-ray these should be used. 
Among these is the leaded screen behind which 
the operator stands during the time exposures 
are made. Such a screen is usually placed in 
front of the controlling apparatus and has a 
leaded glass window, so that the operator can 
watch the patient during the exposure. Lead 
impregnated gloves and aprons are also used by 
some as a precaution, but such extreme measures 
are not necessary for the dentist doing his own 

"With a properly constructed leaded glass tube 


shield, lead diaphragm and lead lined cylinder 
the operator is safe, providing he takes the pre- 
caution of avoiding the direct rays. 

"We all realize that many very useful agents in 
medicine and surgery are dangerous when used 
carelessly, indiscriminately, or may we say ig- 
norantly. The old saying that " fools rush in 
where angels fear to tread," perhaps applies with 
greater significance in many branches of medi- 
cine than we would care to admit. But the fact 
that through the misuse of dangerous agents, 
many patients have met death, or have been sub- 
jected to needless suffering, is no argument 
against their use when placed in competent 
hands. In such hands the x-ray stands today as 
one of the greatest adjuncts to the modern art of 
healing, a blessing to humanity, even if in its 
early history it left its martyrs here and there ; 
its benefits and triumphs far out-balance any evils 
connected with its use. 


Anode, 21 

Arrangement of apparatus, 77 
Alveolar abscesses, 137 
Alternating current, 29 
Ampere, 30 


Broken-off broaches, 111 

Cathode, 21 
Cathode rays, 23 
Crookes, Sir William, 23 
Crookes tubes, 23-21 
Compression diaphragm, 73 
Compression cylinder, 73 
Current conditions for radio- 
graphy, 109-117 
Cysts and tumors, 111 
Coil, 37 

Coil, primary, 42-13 
Coil, secondary, 12-13 


Development of plates and films, 

Developer for plates and films, 

Drying plates and films, 123 

Electrons, 17 
Electric currents, 29 

direct, 29 

alternating, 29 

Electric currents — Cont'd 

high tension, 29 

voltage, 30 

amperage, 30 

wattage, 30 
Electromotive force, 30 
Electromagnetic induction, 32, 

38, 39 
Electromagnets, 38 
Electrolytic interrupter, 17, 19 
Extra-oral radiographs, 83, 93 

Faraday, Michael, 21 
Florescence, 21 
Films, x-ray, 119, 121 

preparation for exposure, 121 
Fractures, 136 

Filling materials, appearance 
of, 110 

Geissler, 21 



Hittoff, 21 
Hertz, Heinrich, 23 
High frequency coils, 54, 56, 5' 
diagrams of, 55 

Induced currents, 39, 10 
Induction coil, 12, 13 

essential parts of, 11 

diagram of, 18 




Induction coil — Cont'd 

illustrations of, 51, 52, 53 
Interrupters, 46 

mechanical, 46 

electrolytic, 47, 49 
Intei -rupterless transformer, 58, 

illustrated, 60, 61, 62 
Interpretation of radiographs, 

Illuminating cabinets, 129 
Impacted teeth, 133 
Intra-oral radiographs, 84 

Leaded glass tube shield, 73, 

Lead compression diaphragm, 

Lead lined compression cylinder, 

75, 151 
Lines of force, magnetic, 35 
Low vacuum tubes, 112 


Magnetism, 32, 33 
Magnetic field, 34, 35 
Magnetic force, lines of, 35 
Magnetic induction, 36, 37 
Magnetic effect of electric cur- 
rent, 37 
Magnet, electro, 38 

poles of, 33 
Missing teeth, 133 
Milliamperemeter, 112 


Nature of the x-ray, 18, 27 
Necrosis, 139 


Ohm, denned, 30 
Ohms law, 31 

Primary coil, 43 
Power rating of coils, 54 
Photographic darkroom, 78 
Plates, x-ray, 119 

preparation of, 119 

care of, 120 

development of, 122, 125 

drying, 124 
Pyorrhea pockets, 142 
Protection from x-rays, 150, 152 
Penetration of x-rays, 27, 113 


Rhumkorff coil, 43 

Rontgen, William Conrad, 19, 20 

Rotary converter, 51 

Rectifier, chemical, 51, 54 

Radiographs, 79, 83 

rules for making, 81, 85, 87 
intra-oral, 83, 84 
extra-oral, 83, 93 

Radiographic examination, com- 
plete, 91, 106 

Radiographs : 

examination of, 128 
interpretation of, 127 
proper tube and current con- 
ditions for, 109 

Solenoid, 37 
Secondary coil, 42, 43 
Self induction, 42 



Spark gap, 70, 54 
Tesla coils, 5-4, 56, 57 
Transformers, interrupterless, 
60, 62 

Tube stand, 71, 72 
Tube shield, 73, 151 
Tube conditions for radio- 
graphs, 109, 110 
Tubes, low, medium and high, 

Tube, regulation of, 111 

connecting to x-ray machine, 

inverse in, 116 
Technic of radiography, 79, 109 
correct and incorrect, diagram 
of, 87 


Unit of electromotive force, 30 
current strength, 30 
resistance, 30 
electromotive power, 30 


Vacuum tubes, 19, 21, 64, 65, 
66, 69 

Vacuum of tubes, how to deter- 
mine, 111, 112 

Vacuum of tube, relative merits 
of low, medium and high, 

Volt, 30 

Voltage, 32 


Watt, 30 
Wattage, 30, 45 

X-ray, defined, 19 

discovery of, 19, 20, 25 
nature of, 18, 27 
penetration of, 27 
effect upon photographic 



production of, 27, 
machines, 43 
tube, 64 

essential parts, 65 
types of, 66 
vacuum of, 66, 69 
connected to the coil of trans- 
former, 69, 70 
dangers of, 145 
dermatitis, acute, 146 
dermatitis, chronic, 148 
protection from, 150, 152 


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By HERMANN PRINZ, D.D.S., M.D., Professor of Materia 
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of Anatomy, Human and Comparative, Kansas City Dental 
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